This applies to casework for the most part. My mantra is, "Patina is OK, filth is not." When a clock or music box is listed as such, it means care has been taken to remove dirt and grime that obscures the original finishes and polishes. Loose case work is cleaned of old glues and reglued as needed to insure solidity as close to original manufacture as possible. I do not replace paper dials if they are still legible unless the client specifically requests it. (A recent client requested I replace a lovely French cartel clock movement with a battery quartz unit only because they didn't have a winding key! I talked them out of it as a key costs $15, less than replacing the movement, and that it would devalue the clock by hundreds of dollars!)
It DOES NOT mean the piece has had its finish removed and replaced. There are extreme cases where this is necessary in order for the true beauty to be seen, but again, I try to avoid doing that if at all possible as it takes far more room and time than I would like for a one-man shop.