Eh, see this is where I don't mesh with that. You keep pushing the idea of intent but it's precisely that intent that I think is missing here.
What I'm looking for is some evidence that Sega made a specific decision to "create" U.S. copies. A new printed insert or some other kind of identifier tailored to the specific copy would be just that. Sure, you could still pick and mix the internals but at least it would suggest that there was a specific intent to actually create a new edition. In other words, I'm looking for something that tells me that when Sega decided to sell Sonic in America they picked this copy, not a copy. Without that clear intent, the intent to not just sell a copy in America, then I can't jump on board. Look at Gyromite. Sure, some copies are actually Japanese PCBs with a converter inside. But the intent to "create" an American game was there. Sega shows me none of that with Sonic.
What if Squaresoft had started taking extra Final Fantasy VII stock from Japan, stuck a UPC sticker on them, and for whatever reason sold them in America? I think it's crazy to then say that there are two distinct "American" versions where one just happens to be entirely Japanese. Hell, if Sonic did get a legitimate release in addition to this UPC nonsense then I doubt we'd be having this conversation at all. Nobody would ever in a million years consider it an American version.
And let's even go further and say there were two identical copies of a game sold in America but the only difference was a different UPC code because of some backdoor wackiness. Let's say Mortal Kombat II or something had different print runs with different UPC codes. I will bet my ass they would be considered mere variants at best, not two completely different games with both being required for a full set. That alone convinces me the whole thing is crazy.