The only thing that I can say about this is that it is in the past and you need to move forward. IMO you are rightfully angry with your
former
vet and what happened. There really is nothing to prove since this is now in the past so looking for a band aide or paper towel or other evidence at this point is useless.
Although you say your dog does not have a rap sheet with the public he now has a reputation at the vets as a biter. My Pebbles tried to bite the tech the last time she had blood drawn and I was standing right there when it happened. They immediately put a muzzle on her and drew the blood~end of story. It was safer for everyone all around and I cannot imagine why this was not done and the outcome was someone got bit.
I spoke to the vet about what happened and he said that the tech did not have a sufficient hold and she had a track record of letting go. Geez what would they do with a really HUGE dog 15 lb dog if they cannot restrain a Yorkie?
I do think that I would let the vet know how upset you are over this entire ordeal and because of this you will not be returning to his practice for further care. This was inexcusable and totally preventable.