Yes, that I've figured it out...I made two simple tests ( besides noticing that nvram file does not exist without game roms ) :
- had 15.000 "coin in" ,
- delete nvram
- back in game and it's absolute 0 everywhere ( new nvram created automatically )
- After some hours of playing, copy nvram at that moment somwhere ( let's say, state of play x ).
- Start game again, ofc 0 again like in test 1
- Put back that nvram previously saved.
- Game back to state of play x ( credits in/out, everything ).
So, basically everything related to chips in/out, payout and stuff, are stored in that nvram file written by mame ( I think ).
So...if that can be editable by some outside means, or not...I'd appreciate it