Abandonware was originally a myth pirates came up with to justify piracy. It then became a common misconception, and I've already lost interest in wherever I was going with that.

Anyway, here's a crash course in the versions of JJ2: 1.21 was the original release, 1.22 is an uncommon release that fixed some bugs, 1.23 is the most common version of the game since any earlier version can be patched to it, and 1.24 is The Secret Files. Any of those versions with an X appended is a Christmas edition, which is basically just the original but instead of the singplayer campaign, it has a christmas episode, and most of the multiplayer modes don't work. It's honestly a bit crap.
You're already familiar with 1.00g(And its rumoured partner 1.00h, which is apparently exactly the same), but then there's also the 1.10o beta, which contains some unfinished levels that were cut from the final game, and then there's the other games that use the Jazz 2 engine: Battery Check, and Animaniacs: A Gigantic Adventure.