If I recall correctly Myth was not just a cracking group (as in ISO release), they did ripping as well. This basically means that you remove some content from the game (or by other means making the game smaller) in order to fit it into whatever space is the current standard.
Unfortunately I can't find a .NFO regarding the release that lists Myth as the cracker... But it makes me wonder if something was ripped here. :)
NB: Only searched here: http://www.nfohump.com/index.php?menu=quicknav&item=sear... -- enter Myth into "Group" field if you are curious about what else they were up to.
Edit This was Myth's farewell note: http://www.defacto2.net/groups/myth/mythbye.nfo which states that they did ripping:
We believe that the rip scene is one of incredible skill. Not only
is there the cracking talent needed to be successful like that of ISO,
you must have dedicated coders and rippers to fully complete the task.
Much time is needed to perfect a rip like that of Neverwinter Nights.
(We'll never forget you old friend)
That said, I am not 100% convinced that this was actually a stolen crack. I'll wait for Rockstar to confirm or deny this (or if someone actually has the original release and does a full diff). I base this mainly on three things:
1) I could not find any release information stating Myth as the release group of MP2. This does not mean much, however. And it was just a quick search.
2) It could actually be a joke by Rockstar. I mean, imagine you sit there with the task to remove the copy protection of the game, you bounce it with your boss he laughs and nods and you throw in that Myth logo.
3) It's also not completely unlikely that the guy recompiling the game had some connection with Myth once upon a time. Back in the day (teenager, very long ago <sigh>) we were a bunch of people cracking games for the fun and the race and the majority of them actually went on to work in the gaming industry.
So, can anyone do a diff of the binaries? :)