It's possible the Aporetics were either dead or fled from the Ark by the time the Inchoroi managed to graft sorcery to themselves. Also Aurang and Aurax weren't the only ones to survive the grafting. There were others. I can't remember the exact number, but it was very small. Like, count-on-two-hands small. It was more than just the twins, though.
Also interesting confirmation that there are Aporetic cants. I always assumed that to be the case, but I have seen others assume that the Aporesis is basically nothing but chorae production.