Actually, U are almost right - the 2004 frame has the new frame but a SHORT mag release.Pre-2004: 'ski hump' guard with short mag release
Transitional-2004: 'no hump' guard with long mag release
Post-2005: 'no hump' guard with long mag release
The long mag release came up in 2005, and the trigger guard has a SLIGHt change to the front of it. So, yes, there is 3 different frames.
I have a 2004 compact and a 2005 fullsize P99 with the longer release.
When the longer release came out, many didn't like it because of the way it looks. But, I will be honest - having the compact and the SW99 with the short mag release - once U get used to the long release, you will definetly prefer it. It is even more convienient.