My 2 cents:

I don't see how anyone could consider a JPN or EU region game imported over here as a USA release because they need converters to play on US region systems. There is no way Sega would have authorized using a 4-1 memory cart on the Saturn or a boot disc on the Dreamcast, that would be Sega basically authorizing piracy since they both have that function in addition to bypassing region lockouts. Gamestop did sell them, sure, I remember them being in stock new. But this was no different than a mom and pop store carrying them.

The SMS had no region lockout, so somewhere Sega saw the need for a couple more games for their dying system and brought over three: Sonic, Strider, and Spider-man. It was easy, no converter was necessary, and they supported what was left of the SMS user base in the USA.

Want another perfect example?

Back in my thrift store days I found two separate copies of Scramble Spirits in the USA imported from Canada for the SMS. I think I even remember a factory outlet selling it new back when the SMS was alive. It is not considered part of the USA region set because it was never officially sold and glitches like crazy when played on a USA system (I guess it is looking for 50Hz vs. 60Hz screen refresh rate). It may be here, but not here in any official capacity.