Okay, after hours of staring... I posit the following:
The white glove and the TFA BTS are NOT the same saber, based on tri-ring position, height of the box rails, and finish.
The tri-ring position does not match the ROTJ or TFA versions, but it does match what's onscreen in TFA. Obviously, the PCB and finish do not.
The depth of the space between the pommel and box section is similar to what is seen onscreen as well-- deeper than the ROTJ version. The TFA version is at an angle that just makes it too hard to tell.
The thickness of the flat edge of the rings is something that varies between most versions of this saber. The only two places we see rings that are even and this thick are onscreen in TLJ, and with the white glove.
Based on that, and the fact it was shown with nothing but TLJ props, I think the white-glove saber was used as the physical saber in shooting the scene in TLJ. That said, it was a composite shot as it included Luke's cyborg hand which would have to be placed into the shot, and his (or his stand in's) hand would have to be removed, leaving detail missing on the prop. So the prop, the box area especially, was heavily retouched in the shot which would explain the different finish and the changing button details (thick to thin, notched to no notch).
I can't say this for certain, but I'm 90% sure....