I didn't look up the release dates, but I think Art of Fighting 2 was the next one, at least of the labeled maps that I have. This takes the original Fatal Fury map, rotates it a bit, and then attaches it to the mainland for a much fuller picture of Southtown.
Here's the map from Fatal Fury 3 which is very similar to the previous one, although turned into an isometric view and made slightly more stylized. This is the one I was working with when I wanted to label my Southtown geography. It was more work than I thought, because I didn't actually know what all the locations were without playing through the game.Finally, here's a map from Fatal Fury: Mark of the Wolves. You can just see the eastern edge of the past maps over on the western edge of this map, so you can tell that all of these locations are new ones to the franchise(s).
Anyway, there's my Southtown geography lesson for the day. I'm actually kinda interested in that because I find weird esoteric details about my hobbies interesting. Plus, some of the Fatal Fury games are among the best in the genre (Mark of the Wolves and Real Bout 2 are the ones in particular I'm thinking of, and lots of other folks would also put Fatal Fury Special on that list) and because Southtown plays such an important role in the King of Fighters franchise, it's interesting to know.