Kat, short answer- from what I can gather, the collective Gibson Bass brains trust don't know. It is the subject of some discussion on other forums.
I haven't pulled mine out of the VP to have a good look at them- I guess I am thinking, why mess with stuff that is working so well? I think I recall seeing pics of them somewhere and they looked very similar from the underside.
They sound very similar when I switch between my Gibson with the Chinabuckers (great improvement BTW IMMostHO) and the VP. at a gig. I will say the VP is ever so slightly "ballsyier" and the Chinabuckered Gibson is ever so "smoother". Although, last night I was struck with how smooth the VP sounded as I was playing Flame Trees- I was playing up closer to the neck than I usually do and not hitting the strings as hard with my finger tips. I would usually use the Gibson for that song.
Anyway, they are obviously both reverse engineered 60s TBird pickups, but whether they are exactly the same and came from the same Chinese factory . I don;'t know. If pushed, I would say- they could be.
The differences are small IMO annd could well be explained by the differing positioning of the neck pickups in the two basses I have to compare them. As you know the modern Gibson TBird's neck pickup is closer to the 12th than the VP and you would expect it to be a bit bassier than the VP. Maybe that is all I am hearing.
The Chinabuckers in my Gibson are 9.2K and I don't know the resistance of the Probuckers in the VP.
OMG we are almost sounding like Jazz bass officionados..
BTW- sell your old Epi and buy a VP you can't go wrong- they sound great IMO. I am enjoying mine so much. Added advantage- the poly finish is pretty tough (compared to the nitro on my Gibson) and I banged the headstock into something last night and it didn't mark it.