There is no "I" in "You"

[Aoi Magi]

A's non-existence at the point of C's existence would be a start...

Bodily speaking perhaps though not mentally so. You're just reissuing the very conundrum of self.

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

Moreover, A can choose self-identify as B even without that merger, relying solely on one's self-identity is a bit pointless.

Sure, in either case though A doesn't have B's personality/memories/experience to draw upon. Would A not be an impostor?

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....?

But looking at it from another perspective, if we are to take A's view of self-identity as truth then it'd mean just the experiences or memories make an individual, but in that case none of A or B's relatives or friends would have memories or experiences of this ((A+B)/2) person and for them it'd be a person similar or quite like the person they knew but not that exact same individual.

??