I have a client that is looking for “code” information about the fire door tag on the service door… when one is missing or damaged, is the door still fire rated…
I would have to say that it is all in the eyes of the beholder at the time of the Inspection.
Label or no Label, rated or not rated, no tag means 20 minutes, painted label, usually you can scratch and see the rating.
Fire rated tags should not be painted over and be accessible for inspection of their rating.
Call it out as unable to determine the rating of the door at the time of Inspection due to the painting of it.
When tag is removed, the door is no longer labeled, and when the tag is damaged, and can not read the rating, the door needs to be identified as an unlabeled door or reported as a fire rating undetermined due to the damage and verification.
Marcel 
If he or she wants the “code” information, the local municipal building inspector should be able to help them out. I have seen tags on frames and on doors. In some cases the tag is on the frame, but the door that has been hung in this frame is obviously not a 20 minute door. Without the proper visible labels, it gets reported as “not verified.”