>>2727168I'd hardly call the soul mere minutia given how large a role it plays not only in Rei's character in NGE but the series as a whole.
The Rei in episode 26 and the "main" Rei in the rebuilds are at least supposed to represent how the Rei from the the bulk of NGE would act in different universes, however different their personalities become.
Rei Q is shown to be a completely separate entity from the main Rei in the rebuild, in possession of a different soul (if any). Calling Rei Q Rei is like saying all the clones in Nerv's basement are Rei when you're explicitly told they are not and only serve as shells for the soul that is Rei.
