Asking this here as its decidedly a Fluff question, and I'm not sure where I would look to find clarification.
We all know that from the Second Founding onwards, Geneseed from the Loyalist 1st Founding Chapters were used to create new SM Chapters. But has there ever been an instance or inkling to indicate whether or not 2nd Founding and onwards Geneseed is used for later Founding Chapters? For the most part, any chapter that is not one of the originals is always declared to be a successor chapter of a 1st Founding Legion.
Is this becuase any 2nd and onwards Founded Legion would not have deviated enough from the 1st Founding Gene seed? but if that were the case, surely "incidents" like the cursed founding would never have been an issue, or indeed may not have happened. We know that every chapter must pay tribute of Geneseed regularly. Is this to act as some sort of Geneseed sample to test if the chapter is rotting from its core?
Any Fluff-gurus know either way on this?
I don't know for certain, but we know that the Mechanicus stockpile gene seed from every Chapter, and that all Chapters ultimately descend from one of the Legions. Thus, in theory at least, there is no difference between Imperial Fist, Crimson Fist or Black Templar gene seed - it's all "Imperial Fist".
As such, with the foundings I would consider the Legions as a "genus" - the gene seed need not come from the inheritors of the Legion's identity.