Blacklight can't prove anything in the affirmative (i.e., that it's original finish). It CAN prove the negative, however. In this case, it looks fine.
I would look for someone who has handled many old guitars who knows what an original finish should feel and look like.
You may have lucked out.
Those pics make the heel look more normal. Thanks
Nonetheless, you do know that while backlighting can help spot a repair, it can't confirm that something has not been repaired. Virtually every person refinishing guitars knows how to make new nitro glow like old nitro.
Having said that, if...
For the life of me, I can't tell.
Maybe it's the lighting, but the heel looks like it has a "soft" edge. It's not as sharp as this one for example:
Any chance that someone could have worked on the heel? (Again, could be the lighting).
Juniors are those guitars that often come up by people who "want to get in the vintage market", and less so by people who actually want to buy a junior for its merits. Like people who jam into a club....not because of the band playing, but because there are lots of people in line. (Let's hope...
I'd say the odds of getting your money back on that are slim.
That's dealer pricing, AND top dollar pricing, in a bubble.
I could (and hope) I'm wrong. Or maybe you should plan on keeping it for 20+ years.