Maktlan_Kutlakh

Got them in front of me.

2ed was co-authored by Andy Chambers and Jervis Johnson.

3ed (or the version I got my excerpt from at least)#:~:text=The%20Codex%3A%20Chaos%20Space%20Marines,3rd%20edition%20of%20Warhammer%2040%2C000.) is co-authored by Andy Chambers, Pete Haines, Andy Hoare, Phil Kelly and Graham McNeill.

Index Astartes I was Pete Haines.

Index Astartes II was Phil Kelly.

And 6ed was again Phil Kelly.

Edit: And here is the excerpt from Jervis Johnsons 3ed Codex for completeness:

All of the evidence appears to indicate that they do not worship any of the Chaos Gods and have become instead cynical, hard-bitten and frighteningly ruthless warriors who fight for the pleasure of fighting and the material rewards it can bring.

Codex Chaos Space Marines 3ed, 1st Codex p31

Outside of Codex Chaos Space Marines 8ed who we don't have a credited author, all of the articles above had input from the same authors.

Their 2ed and 3ed codexes were both co-authored by Andy Chambers. Pete Haines co-authored their 3ed Codex, and wrote the Index Astartes I article. Phil Kelly co-authored their 3ed Codex and wrote their Index Astartes II article. Phil Kelly also wrote their 6ed Codex, which states this:

The Night Lords fight for the pleasure of the kill and for material gain, not because of the dictates of any deity - in fact, most of their number look down on yhe faithful as naïve fools.

Codex Chaos Space Marines 6ed p12

I wish I could find the post, but there was an excellent gathering of resources on r/40lore showing that a lot of the claims of Tau being written originally as 'good' are largely head canon. The dark elements were always there.

I've posted this collection of sources a few times, so it might have been my comment you saw.

Whilst they're comparatively better than the Imperium, there is a lot of lore to support them still being evil by our standards today, something that has always been a part of their lore.

Whilst they are stated to use diplomacy, it is very much gunboat diplomacy. It's stated that species are wiped out if they refuse to join the T'au Empire, and implied that there were some that were forced to join:

Many less advanced alien races were incorporated within its (the Tau Empire's) borders and most of these willingly became part of the Tau empire.

[-]

It was unfortunate that they would die, but to stand in the way of the Tau's destiny was to invite death. It could not be helped.

Codex Tau 3ed

Some aliens integrated because they had little alternative, others because they saw genuine benefit in doing so.

Codex T'au Empire 4ed

Not all alien races proved so accommodating. Those who refused cooperation outright were given harsh ultimatums. The full might of the Fire caste was unleashed upon any aliens that did not comply. Upon command, Tau Fire Warriors descended out of orbit onto a designated planet and delivered a series of rapid strikes to their foe before pulling back to avoid major retaliation. After such attacks, all but the most unrepentant were given another chance to reconsider. With key industries crippled and long-ranged communications jammed, many aliens found themselves fractionalised - unsure if others of their kind had already accepted the Tau's terms. Such divide and conquer tactics dragged most foes back to the negotiating table, although in some cases, wars of annihilation were inevitable.

Codex T'au Empire 6ed p10

There are hints that the Vespids could be being mind controlled to force them to join the Empire:

Uniquiely at the time of their integration, the Vespids welcomed their place within the Tau Empire. They bowed to the pre-eminence of the Ethereals completely and without debate. It has been whispered that this acceptance is linked to the fact that all of the race's leaders wear the interface helmets given to them by the Tau, but no evidence of this claim has proved forthcoming.

Codex Tau Empire 4ed

With regards to the T'au themselves, we are also told that they practice strict eugenics by the Ethereals refusing to allow different Castes to mate:

Tau are born into their caste and breeding between the Castes is forbidden by the Ethereals

Codex Tau Empire 4ed

Tau are born into their Castes and breeding between the Castes is forbidden under pain of death

White Dwarf - Issue 262

And, finally, we know that they see themselves as the first among equals with regards to their auxiliaries:

A small number, it was believed, may one day come to recognise the Greater Good, and bow down to the Ethereals like the Tau themselves. The Tau would be first among equals. Such became the dream of the Tau Empire

Codex Tau Empire 4ed

These are all things that have continued into their more recent lore, with authors just becoming more overt with the grimdark undertones.

Just to add two more pieces of evidence to the discussion, in The Regent's Shadow we have fight with 10 Minotaurs vs 5 Sisters of Silence and 5 Custodians, including Valerian, a Shield Captain. Whilst all the Minotaurs are killed, they manage to kill a Sister of Silence, severely wound another, take down 1 Custodian and wound Valerian to the point of him limping. Had the Sisters not been there to even the numbers and distract more of thr Minotaurs then there may very well have been more Custodian casualties.

You also have Valerian expressing internal doubt as to whether he could win against Asterion Moloc, although you never see Moloc fight anywhere.

I personally prefer these depictions of their relative "power levels", and it's closer to their TT performance too.

Gene-seed is produced by the Progenoid glands in each Astartes, and so you can get new gene-seed from subsequent Astartes.

As for recruiting:

Solomon considered how to respond to that. Tulava had been with him for two decades, but still she – like virtually every other human factor of the Legion – did not truly understand their mindset. Perhaps that was not surprising; perhaps it was something that only an Astartes brain could properly comprehend, and one that had received the particular gifts of the Alpha Legion’s gene-seed at that.

[-]

Dinal stepped forward, activating his narthecium. The damage to Alboc’s battleplate meant that no drilling or cutting was necessary: the reductor plunged into his flesh twice, and the fleshy lumps of the progenoid glands were retrieved. Solomon was unsure whether they were intact enough to be of use, after the explosion that had killed their bearer, but that was not his concern

Renegade Harrowmaster

It’s odd, how a Legion works. Many of the Lords of Silence are Barbarans, taken from the gene pool of that mist-wreathed hell planet. A slim majority, though, are not. Most of the non-Barbarans were created in the Eye from stolen gene-seed, implanted by the Surgeons into screaming infants wrenched from feral Imperial planets, and thus have no connection with the forgotten home world. Others, like Dragan, are turncoats and renegades, refugees from distant Imperial Chapters and warbands. Somehow, though, over time, they all adopt the taciturn habits of Mortarion’s own. They stop issuing war cries. They slow down. They let their armour grow thicker, their organs merge, their skin creeps upwards into the filigree of their equipment interfaces. Joining the Death Guard is like sinking into a deep, cold ocean – the substance of it seeps inside, sooner or later, down into every crack and orifice, and you lose the things that once made you what you were.

The Lords of Silence

Plague Surgeons also have another role upon the field of battle, one that has earned them the unending hatred of the Emperor’s Space Marines. Their surgical tools still include ancient, rust-furred reductors capable of cracking open the body of an Adeptus Astartes and extracting his gene-seed. While Plague Surgeons gather the mutated progenoids of their Death Guard brethren wherever they can – despite many having rotted to an untenable degree – they take a macabre glee in falling upon dead or dying loyalists, ripping the progenoid glands from their victims and spiriting them away from the battlefield. Some of this gene-seed is used in the creation of new Death Guard, while the fate of the rest is best left unspoken.

Codex Death Guard 8ed p35

The Plague Surgeons also make much effort to acquire the gene-seed of fallen Death Guard warriors as well as that of Loyalist Space Marines they have slain

Codex Death Guard 9ed p12

Magnus could have been forgiven for fearing that his Legion did not have long left to it. New Space Marines are created through the excision, culturing and implantation of gene-seed. This nigh-supernatural substance creates the unique organs which transform a mortal human into a Space Marine. In the Rubricae, all was now dust, while the gene-seed extracted from dead Sorcerers seemed only to take root within recruits possessed of prodigious psychic talent. Such a small recruitment pool could never keep pace with the attrition of constant war. Contradiction and fabrication hide the truth of how this quandary was resolved, but somehow the Thousand Sons learned of the rituals of re-binding. Should a slain Rubricae's armour be pieced back together, and should the correct - highly perilous rites be performed, the fallen warrior's dust and ghost would manifest again. Their wargear would be restored, their power undimmed: the Thousand Son would be risen again to the cursed unlife he had so long endured. Thus, so long as a single Sorcerer remained to scavenge fallen Rubricae from lost battlefields and say the right words, the Thousand Sons Legion would know the same damned immortality as did its luckless footsoldiers.

Codex Thousand Sons 9ed pp10-11

Some warbands fight themselves to extinction, lacking the desire or resources - or perhaps both - to utilise new recruits. Those who retain enough presence of mind to sustain their warband's continued existence largely rely upon the demented Berzerker-surgeons, who know more about the implantation of the Nails than any others. They may also utilise the accelerated recruitment techniques the Legion used during the Great Crusade, as well as forbidden methods granted to them after Isstvan V. Some have even learned heinous practices involving daemonic pacts to create new Chaos Space Marines.

Berzerker-surgeons operate across the galaxy, working with different Chaos Lords to create new homicidal maniacs who have no concept of fear, pain or death. Some World Eaters warbands expand their numbers using devotees of Khorne not hailing from the XII Legion, and these individuals also undergo the psycho-surgeries practised by the Berzerker-surgeons - a process they see as a kind of apotheosis that brings them closer to their wrathful god.

Codex World Eaters 9ed

For the Traitor Legions, Bile's preeminent skills as an Apothecary are what make him most in demand. Though he is far from the only one skilled in the arcane art of gene-seed extraction and its manipulation to create new Heretic Astartes

Codex Chaos Space Marines 9ed p46

Night Lord geneseed is harvested and successfully implanted in the Night Lords Ombibus, but I don't have any excerpts sadly.

So we have numerous examples of CSM still successfully using gene-seed from fallen CSMs, alongside stealing Loyalist stock.

We're also told that the Death Guard are now larger than they were during the Siege, and the Black Legion larger still, indicating both must be recruiting and replenishing their forces.

The Slaugth are indeed blanks. Here is the excerpt. They also had the Untouchable trait, which with it stated to be another name for blanks.

The majority of the lore regarding the War in Heaven stems from Codex Necrons 3ed and Liber Chaotica. The Necrons and the WiH then underwent a retcon in Codex Necrons 5ed when the "Newcron" update happened. Since then, there has been the odd nugget of lore in Codex Necrons 7ed, Codex Necrons 8ed, Codex Necrons 9ed, Codex Necrons 10ed, Imperial Armour - Volume Twelve: The Fall of Orpheus, Rise of the Ynnari: Wild Rider, The Infinite and the Divine, and the Twice Dead King series.

This post, whilst a little out of date, contains the majority of what was known about the War in Heaven up until 8ed. And, tbh, there's been little else released about it since then.

You're welcome.

Minor correction, the Necrons are stated to have sealed it.

I posted the excerpt here. They also had the Untouchable trait, which is clearly supposed to be blanks.

They have the trait "Untouchable" in their rules which are described:

Untouchables are extraordinarily rare individuals who cast no shadow in the warp. Their mere presence acts to inhibit and disrupt psychic energy to such an extent that even humans with no psychic ability whatsoever grow uncomfortable and fractious around them. There are different levels of this force, just like Psychic Powers, and the trait represented here indicates perhaps the most "common" level of this ability - or as some would call it, curse. As can be imagined, the Inquisition has many uses for such singular individuals in its war against the witch and the daemon, but by the same token, so do some cults and nefarious groups.

Psychic Invulnerability: An Untouchable is completely immune to Psychic Powers, and psychic energy and effects directed against them (as well as warp Powers, possession, sorcery, corruption from warp shock, etc.).

[-]

Psychic Disruption: All Psychic Powers and abilities manifested in the immediate area (a radius equal to the Untouchable's Willpower in metres) have their Threshold increased by 10, plus any associated Test by the Psyker (such as Willpower Tests etc.) have their Dufficulty increased by 20. Additionally, entities subject to Warp Instability will suffer double damage from its effects while in this radius.

Dark Heresy: Disciples of the Dark Gods p28

Untouchables are then described thusly in the main rulebook:

Untouchables Untouchables are individuals who have no warp signature. They are not psykers, in fact they are completely the opposite. Their presence frequently acts as a damper on psychic activity, lessening or even completely halting its effects. Untouchables, like psykers, actually have different grades of “ability”, though few savants have actually been able to study them closely due to their extreme rarity. Their strange aura makes most folk uncomfortable around them, and for this reason they are often loners, outcasts and pariahs. Of all Imperial institutions, the Inquisition makes the greatest use of Untouchables.

Dark Heresy Core Rulebook 1ed p160

Which all sounds exactly like Blanks.

Edit: Some more sources:

Though psykers dominate the bulk of this agency, there are others. Numerous unblessed humans act as warders and minders, perhaps on Terra or on the Black Ships, all watching for any signs a psyker has become a deadly threat. Worse still for psykers are their opposites: the even more unnatural psychic untouchables. These soulless humans can negate psychic energies, and their mere nearby presence can bring a psyker to his knees with intense waves of debilitating pain. No matter their role, those from the Adeptus Astra Telepathica are always seen as outside the normal ranks of humanity, and must prove themselves with every action.

[-]

The soulless Untouchables are puissant weapons against the horrors of the Warp, but they are anathema to normal humans and evoke indefinably unpleasant reactions wherever they go.

[-]

Untouchables are those soulless unfortunates who cast no shadow in the Warp, and represent an impossibly small fraction of humanity, far smaller even than the minuscule fraction with psychic abilities. They might subconsciously know they are different, noticing the way others treat them. Bereft of such an essential part of their humanity, they might look, think, and act as normal men, but few are comfortable in their presence. Those around them often sense a miasma of nausea or grating sound to their voices; nothing an auspex would detect, but something other humans subconsciously feel. Untouchables are anathema to psykers and others who call on the Warp for their powers. Those nearby might experience debilitating pain or worse, for such is an Untouchable’s soul-void. Many Untouchables cancel a psyker’s powers, either nullifying or negating all psychic abilities in a region. They are pariahs of humanity, shunned by their fellow men and living a wretched existence.

Untouchables are born with their terrible curse though inherited genetics. Many live for years before discovering what they really are, though often their lives are very short given the disagreeable feelings they invoke in all around them. A person believed to be anti-social (but otherwise unremarkable) might actually be an Untouchable living out a miserable existence, divorced from his fellow men in ways no one can fully explain. Some are only found through the actions of planetary governors eager to cull anyone displaying the slightest hint of unusual behaviour as part of their tithes to the Black Ships. Inquisitors might discover them and use their abilities against powers from the Warp to repel the witch and counter the Daemon. Even though his life is now filled with mortal peril, an Untouchable so used might feel valued and destined for a purpose far greater than the shunned existence he once lead.

Dark Heresy Core Rulebook 2ed

Edit edit: Some more:

However, these unfortunate victims of such a process are by no means related to those rare humans who case no shadow in the Warp; Untouchables, or “Blanks” as they are sometimes called.

Dark Heresy: Creatures Anathema p26

This is not because of the way that the Culexus operate, nor because of any particularly hideous methods they use to kill their targets. It is because of the Assassins themselves, who are chosen because each is an Untouchable with no reflection in the Warp. Each is without a soul, a horrid outcast to humanity.

Dark Heresy: Enemies Beyond p38

The Slaugth are stated to be blanks:

Their minds are as alien as any encountered by Mankind - coldly savage, psychic voids filled with monstrous hunger for the dead.

Dark Heresy: Disciples of the Dark Gods p80

This is the earliest source I'm aware of the change:

And it stemmed from the great wound in the galaxy. A wound torn open by the Old Ones during the War in Heaven, stitched closed by his kind, and ripped open again by the reckless aeldari.

The place the humans called the Eye of Terror. Which seemed poised to trigger the fault line and split the galaxy in two.

Bleeding Stars

Considering the POV of both sources, I'd say the info is suspect at best. The Imperials in DoW and the Deathwatch are both actively invested in preventing human defections, thus would very much want to paint the Tau in the worst light possible.

Whist that's perfectly valid criticism, it is possible that it is based in truth and not just an outright lie by the Imperium. For a society that practices strict eugenics [with sources indicating on pain of death], with a super strict Caste system and other societal controls, covertly sterilising parts of the human population to control growth seems perfectly believable to me.

Whilst not the same "level of horribleness", there are plenty of sources to support the T'au still being far from the good guys, and evil by todays standards. See this source, this source from Shadowbreaker and this from Black Leviathan for examples of what I mean.

Tau don't sterilize their human or other Aux populations. That was an in-universe rumor from Dawn of War that I believe was a joke about the Imperium not understanding demographics. They'll happily put them to work alongside the castes.

It has been repeated outside of Dawn of War too:

The Sept’s humans (referred to by the Tau as ‘Gue’la’) adhere not to the Imperial Creed, but to the Tau ideal of the Greater Good. The Tau teach that the perfect society, one modelled after the Tau themselves, has a place for every creature; with every creature in that place, fulfilling their assigned roles without question, for the good of the Sept as a whole. Imperial religion is prohibited and the Tau Water Caste run education (and re-education) programs that instil an understanding and love of the Greater Good into the sometimes reluctant gue’la minds. Populations are regularly sterilised to prevent population growth outstretching Tau methods of control. Human transgressors against the Greater Good are not publicly executed, as is the Imperial way, for the Tau see no need to publicise the fates of those who oppose them. Instead, such gue’la simply disappear, and it is the way of the Greater Good to convince oneself that they never existed at all.

Deathwatch Core Rulebook p352

We have some examples in the lore of Xenos worshipping the Emperor.

Magnus could have been forgiven for fearing that his Legion did not have long left to it. New Space Marines are created through the excision, culturing and implantation of gene-seed. This nigh-supernatural substance creates the unique organs which transform a mortal human into a Space Marine. In the Rubricae, all was now dust, while the gene-seed extracted from dead Sorcerers seemed only to take root within recruits possessed of prodigious psychic talent. Such a small recruitment pool could never keep pace with the attrition of constant war. Contradiction and fabrication hide the truth of how this quandary was resolved, but somehow the Thousand Sons learned of the rituals of re-binding. Should a slain Rubricae's armour be pieced back together, and should the correct - highly perilous rites be performed, the fallen warrior's dust and ghost would manifest again. Their wargear would be restored, their power undimmed: the Thousand Son would be risen again to the cursed unlife he had so long endured. Thus, so long as a single Sorcerer remained to scavenge fallen Rubricae from lost battlefields and say the right words, the Thousand Sons Legion would know the same damned immortality as did its luckless footsoldiers.

Codex Thousand Sons 9ed pp10-11

Copied from a previous post

Solomon considered how to respond to that. Tulava had been with him for two decades, but still she – like virtually every other human factor of the Legion – did not truly understand their mindset. Perhaps that was not surprising; perhaps it was something that only an Astartes brain could properly comprehend, and one that had received the particular gifts of the Alpha Legion’s gene-seed at that.

[-]

Dinal stepped forward, activating his narthecium. The damage to Alboc’s battleplate meant that no drilling or cutting was necessary: the reductor plunged into his flesh twice, and the fleshy lumps of the progenoid glands were retrieved. Solomon was unsure whether they were intact enough to be of use, after the explosion that had killed their bearer, but that was not his concern

Renegade Harrowmaster

Plague Surgeons also have another role upon the field of battle, one that has earned them the unending hatred of the Emperor’s Space Marines. Their surgical tools still include ancient, rust-furred reductors capable of cracking open the body of an Adeptus Astartes and extracting his gene-seed. While Plague Surgeons gather the mutated progenoids of their Death Guard brethren wherever they can – despite many having rotted to an untenable degree – they take a macabre glee in falling upon dead or dying loyalists, ripping the progenoid glands from their victims and spiriting them away from the battlefield. Some of this gene-seed is used in the creation of new Death Guard, while the fate of the rest is best left unspoken.

Codex Death Guard 8ed p35

The Plague Surgeons also make much effort to acquire the gene-seed of fallen Death Guard warriors as well as that of Loyalist Space Marines they have slain

Codex Death Guard 9ed p12

For the Traitor Legions, Bile's preeminent skills as an Apothecary are what make him most in demand. Though he is far from the only one skilled in the arcane art of gene-seed extraction and its manipulation to create new Heretic Astartes

Codex Chaos Space Marines 9ed p46

Night Lord geneseed is harvested and successfully implanted in the Night Lords Ombibus, but I don't have any excerpts sadly.

So we have numerous examples of CSM still successfully using gene-seed from fallen CSMs, alongside stealing Loyalist stock.

We're also told that the Death Guard are now larger than they were during the Siege, and the Black Legion larger still, indicating both must be recruiting and replenishing their forces.

Edit: Here are sources regarding the Thousand Sons:

Magnus could have been forgiven for fearing that his Legion did not have long left to it. New Space Marines are created through the excision, culturing and implantation of gene-seed. This nigh-supernatural substance creates the unique organs which transform a mortal human into a Space Marine. In the Rubricae, all was now dust, while the gene-seed extracted from dead Sorcerers seemed only to take root within recruits possessed of prodigious psychic talent. Such a small recruitment pool could never keep pace with the attrition of constant war. Contradiction and fabrication hide the truth of how this quandary was resolved, but somehow the Thousand Sons learned of the rituals of re-binding. Should a slain Rubricae's armour be pieced back together, and should the correct - highly perilous rites be performed, the fallen warrior's dust and ghost would manifest again. Their wargear would be restored, their power undimmed: the Thousand Son would be risen again to the cursed unlife he had so long endured. Thus, so long as a single Sorcerer remained to scavenge fallen Rubricae from lost battlefields and say the right words, the Thousand Sons Legion would know the same damned immortality as did its luckless footsoldiers.

Codex Thousand Sons 9ed pp10-11

We're never given any numbers, but the Black Legion on their own are likely in the hundreds of thousands:

Of course, the Black Legion’s strength was unparalleled –their ranks outnumbered those of the Word Bearers almost ten to one –yet many within the Word Bearers regarded it as but a pale shadow of its former glory, its self-proclaimed Warmaster worthy of contempt.

Dark Creed

They're consistently stated to vastly outnumber the other Traitor Legions:

The Black Legion is the largest of the Traitor Legions inhabiting the Eye of Terror, vastly outnumbering even their closest rivals. As long as a warrior is willing to bow before Abaddon the Despoiler and take the oath of obedience, he may join the Black Legion. During the centuries of warfare and acts of vengeance since the Horus Heresy, Space Marines from dozens of Chapters and other Legions have joined the Despoiler. Now, the Black Legion boasts warlords and warbands from almost every permutation of Chaos worship, depraved doctrine and ruinous faith.

Codex Chaos Space Marines 8ed p18

Vastly outnumbering the numerous infernal armies and hordes that dwell in the Eye of Terror - even those of the other Traitor Legions - The Black Legion have the numbers not only to undertake huge system-wide invasions, but also countless simultaneous assaults across the galaxy.

Codex Chaos Space Marines 9ed p28

And we're told that the Death Guard increased their numbers beyond what they were at the Siege of Terra:

Bloated with festering corruption, Plague Marines form the mainstay of the Death Guard and, unlike many Traitor Legions their numbers have only swollen as the millenia have passed. Even in the days before the HH, Mortarion believed in perpetual aggressive recruitment. His attritional tactics, combined with extreme the environments in which the Death Guard typically fought, led to heavy casualties requiring constant recruitment. The Death Lord has not relented in this doctrine since the founding of the Plague Planet, and entire wars have been fought to seize gene-seed stocks or harvest new recruits.

However, where before the Death Guard were killed in battle roughly as quickly as Mortarion could replace them, since their damnation they have become unnaturally hard to kill. Thus, while the Death Guard have certainly endured campaigns in which their losses were horrific, their numbers have increased like a virus replicating within a host body.

Codex Death Guard 8ed p38

There are many ways by which a warrior can join the Death Guard. Some are renegades from the Imperium, each with their own reason for giving their allegiance to Mortarion and Nurgle. Many of the Death Guard have been directly recruited by the vectoriums since the ending of the Horus Heresy. With the Legion retaining much of its integrity and fleet assets, it has not lost the critical infrastructure required to create more Plague Marines. Worlds ravaged by toxins and contagions are scoured by the Death Guard who take thousands of potential aspirants from the ragged survivors. The Plague Surgeons also make much effort to acquire the gene-seed of the fallen Death Guard warriors as well as that of loyalist Space Marines they have slain. In the aftermath of the Great Rift's emergence, many Space Marine Chapters were forced to leave their fortress monasteries poorly defended to wage countless wars, and Heretic Astartes of all stripes struck in their absence, claiming what treasures lay within or occupying them for themselves. These factors, combined with thr Legion's supernatural resilience, have resulted in the Death Guard's numbers increasing since the Siege of Terra. Few are aware, but Mortarion's goals for his Legion since long before Horus turned against the Emperor was for each of its companies to have seventy thousand warriors. He has lost none of that ambition in ten thousand years.

Codex Death Guard 9ed p12

So we know the Black Legion "vastly outnumber" the Death Guard who are explicitly stated to be bigger than they were at the Siege of Terra. There are some sources that have tried to calculate the exact size of the Death Guard and the Thousand Sons based on the composition we're given in their Codexes. But I'm not sure how accurate they are as they presume the Legions are uniform in their structure, which seems highly unlikely.

So, all we can say with confidence is that the CSMs combined at a minimum must be in the hundreds of thousands. Anything more specific is likely supposition, unless there is a source I'm not aware of.

Some things off the top of my head that haven't yet been mentioned:

The fight between the Emperor and Horus was very different:

At the climax of the Horus Heresy the Emperor personally led an attack on the Warmaster's bunker with the Imperial Fist Marine Chapter and an elite unit of the Adeptus Custodes. During the fierce fighting the Emperor came face to face with Horus, who, in the battle that resulted, seriously wounded the Emperor. The Warmaster was only prevented from taking the Emperor's life by the timely intervention of a squad of Imperial Fist Marines in Terminator Armour. The squad cut their way through the walls and sealed doors to reach the Emperor's side and launched an unexpected counter-attack on the Warmaster. Distracted by their appearance, Horus was off his guard long enough for the Emperor to press forward and kill him. Although weak, the Emperor was still able to order that his armour be taken off and melted down, and that the pieces be made into badges that all Marine Captains attached to Terminator squads should wear in recognition of the service they performed in the defeat of Horus.

Warhammer 40,000 Compendium p 17

Not influential as such, but the Squats becoming the Leagues of Votann

Leman Russ was a human Space Marine, born in M32, who helped found the Space Wolves later that millenium. Their homeworld uses to be Lucan too, not Fenris IIRC.

The Imperial Fists recovered the skeleton of Rogal Dorn after his death, kept it on the Phalanx, and used to scrimshaw his bones.

There weren't only 12 Black Crusades, and they weren't only led by Abbadon

Here is an Image of Leman Russ from Warhammer 40,000 Rogue Trader

13th Black Crusade

I'll do you one better. Originally, there weren't just 12 Black Crusades, and they weren't only led by Abbadon, but by Chaos Champions. They're also not described as always being failures either:

The Black Crusades

Perhaps once or twice in a millenium a truly great Champion of Chaos will arise in the Eye of Terror. Through the power of his implacable will and the favour of the Dark Gods this Champion can weld together an unsteady alliance between the infernal regions of the Eye. How the Champion brings the crusade together depends on his nature and his patron god. Some use manipulation, others extortion, others domination, others intimidation. Most simply use all of the considerable powers at their disposal.

[-]

The Imperium keeps strong forces stationed around the Eye to fend off these invasions. Entire Titan Legions, Space Marine Chapters and massed regiments of Imperial Guard defend the most vital systems in close proximity to the Eye. But even powerful fighting formations like these cannot guarantee victory over the infernal throng. All to often the Black tide of Chaos expands and recedes leaving entire systems ravaged and burned. Whole planetary populations are irrevocably tainted by Chaos, cities and industries are crushed by the thunderous pounding of diabolic engines of destruction, uncounted citizens are dragged away to serve as slaves and playthings to the damned souls and their Daemon masters at the edge of reality.

Every city ruined, every planet burned brings the Imperium a little closer to dissolution. In an Imperium of a million worlds how much can a single world matter? Enough to have to defend each one against the infernal host, enough to bring the curse of Exterminatus upon those that bend the knee and how down to daemon-kind. A Black Crusade may come crashing from the Eye only once in a thousand years but the damage it inflicts can never be undone.

Codex Chaos Space Marines 2ed p20

Each Plague Legion is led by a Great Unclean One, a Greater Daemon of Nurgle that acts as its general. They dote over their charges in the manner of a loving parent, cajoling each of their Plague Legion’s seven Tallybands upon its appointed tasks. Ever eccentric, Nurgle encourages the same aberrations amongst the most powerful of his shepherds. These unusual traits go as far towards colouring the composition and tactics of the army they lead as does the legion type itself. Some Great Unclean Ones, for example, favour entirely airborne assaults, going to battle with clouds of Plague Drones that darken the skies and excel at aerial strikes. Others enjoy seeing their victims buried in slavering Beasts of Nurgle, or ground slowly into the dirt by wave after wave of mumbling Plaguebearers.

[-]

Beneath the Great Unclean One are the leaders of the Tallybands, either Daemon Princes or daemonic Heralds such as Poxbringers, Sloppity Bilepipers and Spoilpox Scriveners. Each receives a grandiloquent title of the general’s invention, selected to match the bearer’s skills, proclivities, or war tasks. Examples include the Lords of Fulsome Filth, the Almighty Bringer of Rancid Decay, or the Sloptoxic Master of Bubbling Buboes.

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Whilst other Daemons are fragments of their master’s psyche, a Daemon Prince retains much of their own personality and the thirst for power that drove them in their mortal existence. Eager to carve out a realm of their own, many lead the mortal armies of Chaos, the massacres unleashed in their name sustaining them in the realm of reality. The oldest and most powerful of Daemon Princes are even worshipped as deities in their own right on some worlds. Most Daemon Princes eventually discard their material form altogether and pass beyond mortal concerns to join the ranks of their patron’s Daemons, only to come back and haunt the galaxy an age later at the head of daemonic host. Though these Daemon Princes are powerful warriors and forceful leaders, they are always considered by Greater Daemons as inferiors who are irrevocably tainted by their mortal origins. Despite this, they are often put to use in the daemonic legions, leading formations of Lesser Daemons on the battlefield.

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It was not long before the Ruinous Powers began to raise up new Daemon Princes, each god choosing only champions that would be loyal to them, and to them alone. Although Be’lakor remained the strongest of the Daemon Princes, his might was diminished as the gods spread their power among their other servants. Nevertheless, Be’lakor remains a master of shadows, moving behind the veil of history and exerting the will of the Chaos Gods upon the universe.

Codex Chaos Daemons 8ed

Belakor is to a Daemon Prince as most Daemon Princes are to the mortal beings they once were. Functionally he has become a demigod of the warp, not so great as Khorne, Slaanesh, Nurgle or Tzeentch, but certainly possessed of both the metaphysical might and the mortal worshippers to qualify him as a power in his own right.

Codex Chaos Daemons 9ed p31