Numbering system

I've noticed that the numbering system for the DS roms is different from other sites, while the other sites share another common system. Of course I mean some of the games have different numbers. Is there a standard system that everyone uses, or is Romulation just using their own? Thanks!
Post Merge: [time]1272535190[/time]
Sorry, I found the answer to my question. Every site has a different numbering system, which brings me to another question. Is it possible some sites will have certain games, while some other sites don't?

RomU uses their own from what I read before in past questions.There is no standard system apparently.

mario123321 · #1Is it possible some sites will have certain games, while some other sites don't?

Yes
DSi Enhanced games,since RomU doesn't host them