So if my understanding is correct (it may not be, I’m pretty new), Guilliman rocked up to the guy voted “most likely to go off the deep end” in Mechanicus high school and said

“Hey, here’s the keys to the kingdom in terms of modifying Astartes genecode. But don’t use like, more than half of it bc traitors/lost primarchs bad. Oh and if you could make a thing to bring me back to life that’d be pretty sick also.”

And then Cawl just...didn’t mess with traitor/lost geneseed, at all? For 10,000 years? Yeah, not buying that one chief.

To make a long story short, do you guys think it’s possible that good ol’ BC made chapters using partially or fully traitor geneseed?