Help me understand 'XX hidden games' ?

[Franz]

Hey guys!
Sorry for a question that might be a bit stupid, but i have been playing around with RecalBox on a rpi4, and tossed in some roms (no-intro for Nintendo consoles).
e g.
Nes has 615 listed games, but 24 hidden. ? What are this?
I scraped all, and everything went fine, nothing missing. I checked the folders, and i have 615 files in the 'nes' folder.

Are these 24 hidden games from multi-cartridge games like 'Super Mario + Duck Hunt.zip', but the system only recognize one of them? Or are the hidden ones the ones that comes pre-installed with RB?
Or something else?

I tried to uncheck the 'Show hidden games' box, but nothing happends. It still says '615 games, 24 hidden'. I just checked really fast if there is any difference with the box un-/ticked but i can not see any roms dis-/appear.

If the hidden ones are broken roms or something like that, is there a easy way to find them for removal? Like marked in gamelist.xml or something?