The percentage on a chocolate bar’s label refers to the combined percentage of cocoa mass and cocoa butter, but doesn’t break it down further. Cocoa mass is responsible for deep, dark chocolate flavour; cocoa butter is responsible for richness and melty mouth feel. A good chocolatier will blend the two to bring out the best flavour of the cocoa mass while still presenting a silky smooth chocolate.
So while a high percentage chocolate bar doesn’t guarantee that you’re actually getting more cocoa, it does tell you that that there’s less sugar in your chocolate. Depending on your palate, that might be a good thing or a bad thing.