sigh Given the all knowing being that Aizen made himself to be, we can take Ulquiorra's words literally. I.e. When he said "even Aizen hadn't seen it yet", he meant - Aizen hadn't SEEN it yet. NOT Aizen didn't know about it. So mostly like, Ulquiorra was 4th WITH his second release. Hard to believe I know but there is no evidence but speculation that Ulquiorra was incorrectly ranked. I mean, even after feeling Ulquiorra's reiatsu in his seconda etrapa, Yammy still went on to bad mouth him. but this is still a possibility seeing as he beat ichigo hollowfied while Yammy had trouble with ichigo