User blog comment:Khalael/Canon Discussion 4: Sensei, Perpetuals and the Illuminati/@comment-2253300-20140911004853/@comment-1620907-20140911072134

On the note of Perpetuals being the replacement for Sensei, it's hinted at very strongly that some of them as biological sons of the Emperor. Of course, the Primarch Vulkan is also a genetic son of the Emperor who is a Perpetual, but the reasons for that haven't been explained, seeing as he's the only Primarch (so far) that seems to possess that trait.

As 40k moves on in editions, more and more of the older lore seems to end up being phased out, so that may end up being the case. Black Library has even started acknowledging certain works as Old Canon as part of their republishing of classic stories. I hope this helps clarify things, Remos.