About this dick rubbing camp, is it invitation only or can anybody stop by, and yes I'm inquiring on behalf of a friend
Slaanesh welcomes you.
Also remember that Thar Ariak Hraldir of the Space Wolves was actively trying to remove their flaw from the Canis Helix, via the Tempering, in order to create a legit "Legion" size force of chapters surrounding the Eye of Terror...and then Magnus came by and said "NOPE" and wrecked that.
I'm not sure how much I enjoy the fluff of these new primaris marines, I prefer that Crawl just (re?)perfected the art of creating Adeptus Astartes that had begun to deteriorate since the end of the Great Crusade.
Thinking of it like this, then all of what we know of as Adeptus Astates in M41 is simply a shadow of what they used to be. Which I think is very plausible given how mutated/corrupted the gene-seed, of each "legion", has become.
Also if we wish to push the envelope this way perhaps the gene-seed of the traitor legions were cleansed of whatever mark Chaos left upon them so that future chapters carrying the gene-seed of Fulgrim, Perturabo, Curze, Angron, Mortarion, Magnus, Horus, Lorgar, and Alpharius can be used once again - since the geen-seed vaults on Terra is stocked full of these.
Lastly perhaps even resurrections of the II and XI legions could return...