I'm getting your thoughts here mr OP.
Your referring to your chaos grey knights as beeing grey knights MK 1, an experiment that failed.
It didn't meet the specifications (ie, all of them got corrupted at once, not very succesful)
So the imperium excomunicated them like the flame falcons.
The flame falcons was (for the ones that don't know) a cursed founding chapter that after a battle ignited with strange flames.
It didn't hurt them and the falcons thought it was a gift from the emperor and feasted in celebration.
The grey knights, did not. The grey knights followed their orders and exterminated the entire chapter.
A few flame falcons is rumoured to have gotten away, feeling betrayed by their imperium, and with burning bodies, theres no real way of coming back.
Anyway, you mean that your chaos grey knights would be grey knights MK 1, and the grey knights that have never suffered a single brother to fall to chaos are grey knights MK 2.
This thought isn't really that bad but the others didn't really think of it as soon as i did. (Or perhaps you did, i began thinking he meant it at my last post.)