My brain isn't working right now(Tiredness), so out of curiosity, what is the cheat code?

Anyway, Jazz 1 had a cheat code("APOGEE") that activated "Apology mode", which would reduce the game to 16 colours, and slow the game down to a crawl. This was poking fun at Apogee releasing 16-colour games that ran really slow at the time, even though games like Jazz 1 were possible.
The code was taken out of the game some time after the initial floppy release.

Jazz 1 was originally to star Wubbo Ockles, the first Dutch citizen to go into space.
After it was changed to Jazz(Named after Cliff Bleszinski's dog, who himself was named after the Transformer), he originally looked very different and was purple. He was then changed to green, and then later redrawn by Nick Stadler(The earlier green version can be seen here).

It's possible that the Jazz 2 source code no longer exists in a usable form. A while ago, there was a possibility of it being released, but they couldn't find it, and lawyers started getting in the way(Although it's academic at this point, since all the source code could really do now is help to optimise some of the Plus code, but not really anything else).

Jazz 2 was originally to have a 3D sequence between episodes. This was even partially coded, and an easter egg in the game(Press 'I' on the Orange games logo, then try stuff) is theorised to be a test of what was finished of it.

There is a code displayed at the end of Christmas Chronicles '99 and Holiday Hare '98. Since the code at the end of TSF, when entered into Project 2's website, would give you some extra levels to download, it is assumed that this was also planned for the Xmas editions, although HH98 came out after the site closed down, so we don't know if any such levels were even designed.

There are two versions of Jazz 3D floating around. One is an earlier build with a simpler main menu, and the other is a later build with a voice saying "Welcome to Jazz Jackrabbit 3D!" on the main menu.
Additionally, a partial production diary from Jazz 3D's development is featured in at least one of these builds.
Also, both versions say "Jazz Jackrabbit 3D public beta test" on the installer(Or setup, I forget which). It is widely known that both of these versions are early, unfinished, buggy alpha builds, so make of this what you will.
Finally, no one knows how Jazz 3D was leaked, or who leaked it. My personal theory is that either it was sent to an Epic employee who then sent it to a friend who sent it to a friend, etc. until it ended up on torrent sites, or that a copy was stolen from Epic's offices.