You're right about the A designation., In the shop we always referred to the refit as the A. Same model, different ILM paint job.
I was lucky enough to examine the original model, the 8 footer or however large it was, back when we had the job at Foundation Imaging of doing the FX for the Director's Cut of Star Trek: The Motion Picture. It's an astounding piece of physical modeling. I believe it had the A designation on the saucer by that time. I was on another show when that job came through. I asked to be switched over. No dice, not senior enough at the time. I was bummed about that.
As for the Firefly textures, that is the model we used on the TV show, not the film, which was done by Pierre Droulet. The LW model, which was repainted for the movie with enormous UVs that caused all kinds of grief for Lightwave at the time, is buried Lord knows where in Zoic's archive. So this was the only one readily available. Doesn't look too bad considering it's from 2002 or whatever.