Where do exchanged soul fragments reside? Are they appended to the akashic record with a person’s soul signature attached?

This is exactly the case and a nice description of the mechanism involved. It is an exact representation of the event in question leading to the fragment being formed. The term “soul fragment” is a metaphor representing an energetic signature of an experience with the soul signature as an element defining who took part, and it has the signature of all involved. This is the way, in going to the akashic record, it becomes clear to the host the sequence of events, and the energy of those parties being an element allows the host to recognize them once again when they bump into one another in life. Or in the case of a spirit coming along who the person has known in prior lifetimes, there is often a soul recognition and it may well come via the soul fragments within the akashic record of the individual, and then they will be more inclined to interact once again with an old friend or enemy.