I think your reasoning is sound, and no doubt we would all like to know now merely appearance, but the provenance as well as any and all work done in the interim. I'm not suggesting these things aren't material, and perhaps even the most important information (assuming it's available). I am suggesting, however, that it's not well covered by the word "mint", which only refers to appearance and not history.

If I purchase a watch from someone, the best I can hope for is that they've provided me with accurate information. I generally believe they do, but I also believe that most of us don't know any more than what the previous owner told us. We could be perpetuating truth or falsity, acting in complete good faith but without any way to verify it. What to do?

The analogy to classic cars may be imperfect, but not terribly imperfect. If your definition of "mint" refers to more than appearance, than it's really not a good word to describe what you are seeking to define. Mint is used as an expression of appearance in many objects, and perhaps the answer is to have another word to refer to the other aspects you are hoping to include in your definition.

Scott