Is nobody considering the possibility that these are NOS Bally backglasses, just from long after the game was made, when there was enough demand that they were forced to do another run of them?

When the original run was done, Paul Faris would have been all over the process, making sure everything was done and redone and tweaked specifically to this art to make it look like his vision. If there was another run done a few years later, it would have just been some guy from Purchasing or Parts Sales coordinating with the screening vendor to ship them the films, which would be run in whatever their current process was, with any institutional knowledge of Centaur-specific tweaks long gone. My dim recollection is that something similar happened with Williams Black Knight blackglasses - there were the original ones, then there was the run done by Parts Sales a few years later, and they're not quite the same, but they are all "NOS Williams Black Knight backglasses." In both these cases, we're talking about gorgeous wall-hanging-worthy art, so there would have been demand for more glasses beyond the normal handful that are ordered to replace broken ones.

I'm checking with Jim Patla to see if he has any insight into this.