I'm up to level 82 on a replay and just watched a scene where Fandaniel says that even as a mortal (Amon) he had a recurring dream similar to Zenos's dream of Amaurot - I think in hindsight we are supposed to assume this is a dream of Elpis, perhaps specifically of the wiped memory that drives Hermes to despair.

Additionally, upon being raised to his position as an Ascian, he would receive the memories from Fandaniel's memory crystal, which are not actually Fandaniel/Hermes' own memories but an impression of him as remembered by Emet, Lahabrea and Elidibus after the Sundering.

Adding to this, we have the information that forgotten memories are regained after death - I'm not certain whether this is meant to include all past lives or just their immediately previous life, but I think it's meant to be all of them. In that case, "Amon" as we encounter him in the aetherial sea seems to be a mix of Hermes' memories and the determined-to-be-independent identity of Amon, but it's still unclear and we are interrupted by Asahi before we can try to appeal to Hermes' original nature.

(Though come to think of it, Asahi seems to be Asahi and not some amalgamation of any past lives he might have had - though perhaps in cases where each life of a person's soul has the same basic personality, it just takes the identity of its most recent life and there's no struggle between them...? This is all incredibly theoretical still, even though we've had glimpses of how it works.)