>>2327124I mean that it's based in the fake city Homulilly created. All of those "flashbacks" never actually happened. Being generous, at most they existed as memories implanted ONLY in Mami's manipulated mind, since they never ocurred and Bebe's memories were left untouched.
Truthfully, all of them were not much more than a month or so inside the barrier. Mami remembers meeting the rest of the girls a long while ago, surely more than that. Thus, those parts where Nagisa comforted Mami while she was alone and all that couldn't have possibly happened, and she would have no reason to think they ever did.