Yep, i think X is just another PAL region code, at least that's how i interpret it in my apps.
There's no such thing as a region free game. But there's no such thing as (working)region lock either. The disc channel checks for the region of the game, and that's it. If you use a loader, it ignores the region, or better only uses the region to determine which video mode to use. If you can play certain games even if they are from the wrong region, this mostly has 2 reasons:
1. you have a good tv/cable combination that just eats PAL and NTSC
2. the game has video modes for both included
Maybe you saw this already, you tried to force a game to NTSC or PAL, and it immediately froze with a green screen. This usally happens if NTSC or PAL video mode is not present on the disc. If you don't force the game then, it runs either perfectly(good tv) or in black&white(bad tv, >90% of cases NTSC sdtv).
Ok there are exceptions to the region free, but until now it's only NTSCJ or KOR something else as far as i saw it.