The short version: while Sonic 1’s official release date was June 23rd, 1991, several Usenet posts around that time make it clear stores in various parts of the US were stocking it up to two weeks beforehand. (There’s also some discussion of pre-release coverage of the game, if you’re curious.)
It’s an interesting look at an era of gaming where synchronized, nationwide release dates in America weren’t really a thing. (As the article notes, it took quite a bit of planning to get the sequel out on “Sonic 2-sday” across the country, and even then didn’t immediately become the standard.)
We had the exact same discussion with Pac-Man for the VCS some years ago. There was an official “Pac-Man Day” where the release was celebrated, but we found several new stories about it being bought out at different retail locations before then. I even wrote an article on the ephemerality of release dates. Nothing’s ever tidy and simple!