U.S. Sonic with UPC sells for $981.33

[TonyTheTiger]

But with Sonic, there was no other release of it here to be a variant of.

It's a variant of the European version. Pretty simple, really. Just because there wasn't another Sonic release doesn't magically make this variant an American copy. That's where I think you're missing the point. You can't cherry pick and say that if MKII had two different UPC codes then they'd just be two American variants but if Sonic gets two UPC codes then one is European and the other is American based solely on the fact that there was no actual American release. That makes no sense.

Besides, if you're saying that the altered UPC code makes it a wholly different release, are you saying the opposite holds true, as well? That if two versions of the same game have the same UPC code then they are the same release? Because that seems to be the gist of your argument against Radiant Silvergun. The UPC codes are the same so it's the same title.