The idea that "everything has a part number" is generally correct but has a few exceptions. You won't find serial numbers (or often, part numbers) on small cons

The idea that "everything has a part number" is generally correct but has a few exceptions. You won't find serial numbers (or often, part numbers) on small consumables, like washers, or things like rivets. But it's very common for bolts to have part numbers. Something as large as a flaperon would definitely have a part number (which would tell you if it was part of a larger assembly), and might be serialized and directly trackable. Disclosure: I don't work on commercial aircraft, but I do work on military aircraft.