Mr H, of tunes I know and have tried in the past, I'd be inclined to say the MIDIs are pretty reasonable transcriptions. Where there have been differences to what I know as "the tune", my inclination has been towards different people knowing different versions - something that is impossible to check without both knowing the source and having that material to hand.

There are/were a few bad MIDIs in the Mudcat online version (something I think is bound to happen with what I presume was a block conversion of several thousand) but they were tunes that say wouldn't play at all with Windows Media Player. Very occasionally, there was a request for help on one of those. I could "fix" them in Cakewalk which would read them and allow me to edit out the "crap" to give someone a working version.