Does original Xbox games are region-locked on X360?

Hello, Gamespot fans!
I got few question in which I can't find clear answers. So, today I got CoD Finest Hour and GTA SA (both are from US region and my X360 E\GO comes from EU, bought in Germany). Tried playing SA and it gives me an error ( because of different regions and blah blah blah), when without hope I launched CoD and I was amazed - it worked. So question is: how to know which original Xbox game from other region (NTSC presumably) will work\compatible on my X360 EU? Maybe there is some kinda list to look at?

Thanks for answer and sorry for my bad language.

So, any help would be nice..?
I only found this one: http://gaming.wikia.com/wiki/Region_Free_Xbox_360_Games But nothing more solid.