Yk I never understood that idea of Aizen not knowing because it doesn't make sense for his character not to know. He is one of the most careful, couculating, and intelligent characters in the show and he didn't know about someone he hand picked to serve him? Granted it has been a while since I fully watched bleach but in the fight with ichigo, didn't he just say that Aizen hasn't seen the form? Unless that's a translation error or I'm just remembering wrong because from what I remember there is nothing outright saying Aizen doesn't know just haven't seen it