aizen is like a friggen mega data processing computer i wouldnt say he knows every thing but at the same time i wouldnt say he dont let`s say we have 2 shinigami`s aizen knew the ability of the first one,he will analyze and process all the possbilties or let`s say 99% of it so we can say he knows every thing but he dsnt know the ability of the other one so he have 0 data to analyze so he will not know what is coming next . aizen is not omniscient
