Well, there's NEVER been a set, neat criterium. It might be effected by genetics, for all we know. Or personality. Some people got memory loss, some didn't. That's all that matters.If that was the case then so would Tenrow wouldn't he since he was also an AIDA victim? I guess they could have been one with the AIDA. Did either Yowkow or Tenrow say anything to imply that they were watching Haseo? And then why were Sakaki and the kids not? They (except for Sakaki as his was complicated) were all AIDA victims too right?
Well anyway here's another thought. If Haseo really doesn't remember the World then who was the "friend" who told him about it. Was it just subconsious memories of his that he wrote off as a friend's conversation or was it somebody?
as for the "Friend", it might've been an excuse he made up on the spot.
It's not Wikipedia, shut up.wikipedia.com, then look up sora = Haseo.