Ask the people @advanscene why they (supposedly) have non-public releases in their dats... I don't understand that, either.
I actually use No-Intro dats for managing my ROMs.
No-intro has the same , there are also releases in their dats that are not to be found anywhere.
See here :Current MIA No-Intro, just for update information:
Commodore - Amiga: 348 sets & 528 roms miss (348/3151 - 528/5752)
Nintendo - Game Boy Advance (e-cards): 10 sets & 11 roms miss (10/3080 - 11/4324)
Nintendo - Game Boy Color: 3 miss (3/1418)
Nintendo - Super Nintendo Entertainment System: 1 miss (1/3395)
Sega - PICO: 6 miss (6/329)
Sinclair - XZ Spectrum +3: 3 miss (3/130)
There where more private games in the advanscene dat before , now only a couple are missing.