There is no "I" in "You"

[Aoi Magi]

What conundrum? I am simply stating what I've already stated before.

What constitutes the self.

In order to be an imposter A has to exist. In the first case A doesn't, in the second case, yes A is pretending so can be seen as an imposter. Your point being....?

Does the transfer of A's memories/experience to B render A non-existent?  If so, what's transferred to B?

... umm just A's memories and experiences are transferred to B's body. You wrote that yourself, why are you asking me?

And did you not read anything I wrote so far?

'self' is the collective summation of all your memories, experiences and all of the factors creating and effecting them including physical attributes.