How is it that the Founding or Heritage of a Space Marine Chapter is unknown?

Question

I like watching 40k Theories videos on YouTube and they regularly look into Space Marines Chapters, most recently the White Templars. One recurring thing that comes up: from an unknown Founding and from an unknown Source (i.e., the Primarch is unknown). How is it not known anymore in which Founding the Chapter has been created and who the Primarch the Gene-Seed had been taken from is?

I can understand (somehow) that it might be lost with the Administratum. But still, there are 1000 chapters. It should be quite easy to keep the paperwork together when the chapter was founded and who the Primarch is. Specifically, since this all happens on Terra (to the best of my knowledge) and therefore, there is no problem with sending it there, where it might be lost on the way.

Answer 1

The out of universe answer is to allow players to use the colour scheme and name of the chapter while not being prescribed to which army book they have to use. GW also likes to keep players own options open as to the stories they want to tell about the armies they create. So if a player for instance wants to create a loyalist chapter and say they are formed from the remnants of a traitor legion that didn’t turn in the heresy they can.

In universe yes the 40k universe loves its admin, but it is also very inefficient and the nature of a chapter, constantly at war, means that records and information can easily be lost and destroyed. Also the primarchs had gone into legend (pre robute resurection) and the lessons of the heresy meant that various agencies wanted to prevent chapters forming back into legions, so you can imagine that some new chapters are purposly kept in the dark as to there legacy, Gene seed has been taken and used to make them, they don’t need to know who’s it is. Another thing to note is that the Gene Seed changes slightly with each new founding, so a 3rd 4th or 5th generation chapter may actually be, genetically, far enough removed from its founding chapter that it can no longer be called a successor of that original source.

It might also be possible that some of these chapters are made up of a variety of different gene seed liniages, imagine a new chapter being founded in the midst of war from a group of different chapters offering up gene seed, these chapters may come from a variety of sources and so the end result is a chapter made up of 20% salamanders, 60% ultramarine and the rest whitescar.

In the war of the beast series there is real horror that the chapters formed out of the imperial fists have protocols in place to reform as a single force in the event of a real threat to Earth. This demonstrates the very real fear that a series of chapters with the same lineage may converge back to a single legion.

The only founding chapter that is very protective of its legacy is the chapters is the dark angels so you can guess that these legions are probably not formed from them.

For further information

https://www.warhammer-community.com/2016/11/16/rites-of-initiation-the-making-of-a-space-marine/

In this article it states that all chapters give 5% of there geneseed to the Mechanicum as a tithe to be used for the creation of future chapters. In this case it is possible that the chapter is never told what there legacy is and which chapter there geneseed originated from

Answer 2

To add to @RicardC great answer - sometimes ignorance is bliss.

After the Horus Heresy, quite a few members of the Traitor Legions remained loyal - they abandoned their old legions becoming Blackshields. With time, some of them turned into new Chapters that don't know (because they don't want to) about their origin. For example, it is very strongly hinted that Blood Ravens are descendants of Thousand Sons. In a similar fashion, the renegade (but not traitor!) Soul Drinkers Chapter always believed that they are descendants from Dorn and Imperial Fists, just to find that it is not true - somebody decided to lie to them to hide the truth that it was most likely one of the Traitors.

Finally, there are the mysterious two missing primarchs, that were lost and forgotten even before the Heresy - while it has been hinted that they've been originally absorbed into Ultramarines Legion, they could have been turned into new Chapters.