Yes, it's kind of weird, but it does indeed make sense at the same time
First off, we should go over the fact that Sumeragi's Weaponizing Grimores do indeed enhance a Septima... I think, and the one Tenjian used was simply not as good as the original.
If you didn't play LAiX, I'll fill you in. So there's this character from that game called Blade, she has the Azure Striker Septima, just like Gunvolt, but not just like Gunvolt, scans show (Sleepy has already provided them, they're somewhere in one of the pages) that her Azure Striker Septimosome comes DIRECTLY from Gunvolt's very corpse (LAiX takes place 100 years after GV1 Bad Ending).
Blade was captured in a human raid against Asimov, the latter in turn captured Blade and implanted the Septima into her (she could not have been gone for long, considering that her sister kept a picture of her and herself, and Blade didn't seem to noticeably age.)
How this relates to scaling to Gunvolt 2 is that Copen in this game is essentially, his Gunvolt 2 self, same moveset and everything. Blade has the same Septima as Gunvolt, from Gunvolt 1, not 2. Blade also beats Copen twice, and draws with him once with this GV1 Septima, and not even using it properly like its former user. Thus, GV2/LAiX Copen is = Gunvolt 1 GV/Blade
I know, kind of weird, but it does make sense