Then I guess you agree. Current Allen doesn't remember what happened in the past (or it isn't familiar to him), but it might be that he saw a memory of past!Allen's. In that memory, past!Allen and Nea were meeting for the first time. If so, then judging by what Nea said at the time, past!Allen might have memory/stability problems as well.
When Nea appeared to speak to the Earl in 182 and 189, those weren't memories. That was Nea, and he knew what he was doing. However, when Allen passed out after Tyki pierced his heart, when Allen was told to play the piano on the Ark, and the part we were just talking about from chapter 198, what Allen was seeing at those times might all have been memories belonging to past!Allen.
I agree only with these two moments:
After tiky pierced Allen's heart, in Allen's dream, Nea says:
''Not, not yet''. Ok, its nothing wrong, Nea was saying something to PastAllen, to wait for something.
During Allen was in the Musician's room, the difference is that Nea wasnt talking to PastAllen, but to other(s), because he talks about Allen in 3rd person, for example,
''Its Allen sheet music''. But yes it all makes sense, a memory of PastAllen meeting Nea and someone else.
But with this moment, no:
Chapter 198, again, I see its not memories of PastAllen because the past tense he uses when he says:
''And Allen, you as well... ... You too have become (or became) a broken doll''.. If it were a memory of PastAllen, he would say this way:
''And Allen, you as well... ... You too will become a broken doll''.. Because he obviusly was talking with PastAllen... I mean, PastAllen has not yet become the host of Nea... or whatever Nea means. Summing up, if it were a memory of PastAllen, why Nea was talking in past?
It is like a friend says to other ''You got married'' and the friend has not get married yet... (simply quickly example).
Still not sure what to make of the Shadow thingy, but it does seem to relate to Noahs/Dark Matter since Skinn Bolic and Tyki are shown to have their own as well.
Excuse me, do you remember when this is said?