Board Thread:Warhammer 40k General Discussion/@comment-202.67.108.41-20140425072251/@comment-24944355-20141119005640

Your wrong, true the bulk of the loyalists of the Sons of Horus, World Eaters, Death Guard & Emperors Children were killed at Istvaan but there a fair number who were not with the fleet at the time being on assignments else where some of these would have stayed loyal. Also while the Word Bearers had long since removed any possible loyalists from their ranks the same could not be said of the Night Lords, Iron Warriors & Thousand Sons all of whom would have had loyalists that were not purged. Even the Alpha Legion would have had a few that refused to join the rebels perhaps even by Alpharius design. But it would have been especially true of the Iron warriors who canon says had an entire taskforce that was out of contact & new nothing of the heresy until they stumbled into an Alpha Legion operation & ended up at war with them on the Emperors side (besides NOBODY really like Perturabo even his own legion)

In the end their would have been thousands of Loyalists from among the traitor legions many of whom would have survived the war to be rolled into 2nd founding chapters with their true histories deleted to avoid the suspicion & hate that would have followed them. So any 2nd founding chapter whose origins & primarch remain a mystery, like the Blood Ravens & Silver Skulls, could very well of loyalist stock from traitor legions.