It seemed like it was common to submit videos from machines you owned, played in your home. Thing started getting a lot more serious, for reasons unknown, and you had to start getting machines preapproved, etc.If I'm not mistaken there were questions brought up about the Donkey Kong boards that Mitchell used in some of his real hardware runs. Nepotism was rampant in the game records community, and there were instances where judges allowed him to use his own boards. I'll have to look it up.
There was some controversy about one of his boards, and I think a record not approved because of an inexact repair (capacitor replaced with a similar value instead the stock value, IIRC) or maybe it was donkey kong roms swapped into a newer board or something. I don't expect it was malicious; this is how arcade boards are --- Billy doesn't seem super technical; he probably could check that it wasn't a bootleg board, but he may not have known he needed to be very specific about anything more.
On the mame thing. The more I think about it, the more I wonder if he was playing on one of the multigame jamma boards built around mame; but I haven't checked if that timeline makes sense. I ran across a forum post from 2009 discussing them, but didn't look that hard. He probably should have known if he was using a multiboard instead of a real board, though.