As someone that had it pass their hands on its way to you, here are my observations:
1) The tape in the bubble looked and felt like other bubbles I have with worn, dried tape
2) It looked legit and not re-taped to me
3) the tape I have seen on my loose bubbles is incapable of holding anything to it again - too dry - so unless they added glue to the tape, I can't see how the gun could be holding on right now - I didn't touch the tape 'sticky' side when I had this, but it did feel dry overall
As for the blaster being a V7 which so far is only confirmed on Euro cards....
As someone who has spent a ton of time this past year finding combinations of figures/accessories/weapons confirmed to cardbacks, I have to say it is plausible.
Up until my research, no one pointed out that a black/blue Leia Blaster was ever confirmed with Leia Bespin - all accounts said blue only, so new things still can be found each day!
The problems are there aren't many people that are doing that type of research on basic Kenner figures and even a quick look around the net right now, the pictures of the blasters found on Boba 21 backs are impossible to see the tell tale raised bar. You could spend hours and hours searching and never find one clear shot. Unfortunately it is an angle most people do not take a picture of and even if they do, the gun might be taped in a way that the bar would be out of view in the shot or loose upside down in the bubble.I find it odd sometimes that people focus so much on the COO markings of the figures, but only care about the proper accessories and weapons on difficult or hard to find figures, leaving all their basic, straight Kenner figures all crazy kimbo with whatever fits the figure (no offense meant to anyone!!!! just a little strange to me ).
Anyway.... To really figure this out you will need some time (or luck) and find Boba MOC and focus collectors and have them check the 21 backs specifically for it. And even then it still may not be confirmed at all (oh and dented, yellow bubbles or AFA cases make this very difficult).
Boba was a huge figure being produced and that blaster wasn't just his, so I would guess that each factory had a couple molds cranking them out at the time.
To just dial in the existence of a V7 back in the early US Kenner days, you could open the scope to look at any MIHK 21 back MOC with an Imperial Blaster (slight problem there is I am sure more than one factory printed the MIHK on it and I am sure only factory would have had that mold if it indeed existed back then).
But that would increase the possibilities of confirmation greatly.
I hope you can get a confirmation of it since that would be a great piece of info for collectors but those selling the V7 blasters at slightly higher prices won't like you if you do.
Good luck, Stef!