User blog comment:Khalael/Canon Policy Discussion 1: Space Marines/@comment-4608429-20131105174533/@comment-1620907-20131105203924

On the issue of the Traitor-Loyalists. I don't think any loyalists should have the geneseed of a traitor legion no matter the reason. It simply would not be feasible due to the suspicion that is held for these fallen legions and the fears over their geneseed being tainted. A chapter loyal to mankind or the Emperor could only feasibly originate from a chapter that had the geneseed of a loyal legion, for that is the sole manner in which they could have properly come into existence. Space Marines that have decided to shun the Imperium while not falling to Chaos or ones who have been cast out by their brethren despite their conviction, have to have been approved by the High Lords of Terra in the first place. I highly doubt that geneseed from a traitor legion would have ever been permitted for use in the creation of a new chapter.

As for the Lost Legions and the ATs issue. That is a good point that should be saved for another discussion, as ATs are an area that will be looked in greater detail at a later date. Likely as an Alternate Timelines Policy Discusion once the Canon Policy has been solidified. I do appreciate you bringing that matter up, as it will make a good point to be debated.