The release groups tend to use the 8.3 naming convention (an artifact from BBS days) or a slight tweak thereupon with the first 8 chars being the name of the group followed by game and region or maybe just part of the roms header, the next usually being zip.

The numbers are added by the site you are looking at, for instance GBATemp has one, ADVANsCEne another, pocketheaven yet another, GBARL another and your roms may come with another numbering list........... The numbers frequently match between sites although they may not (some sites include the game and watch for DS or in the case of GBA stuff like codebreaker dumps).