I understood that the reason for numbers on the outside was to make the numbers accessible to Law enforcement officials or anyone else such as fire departments who might get a call on a found drone. The fear was that a drone might be booby trapped and explode when the battery was removed. As a Police Officer and a drone flyer I contacted the FAA local office where I serve and just asked what the procedure was identifying an owner by number in case I got such a call on a downed of found drone. I was informed there was none yet. The FAA official I spoke with said he did not know any way of looking up ownership by number. As a Police Officer I can run a vehicle tag on OLETS or NCIC and identify the registered owner of a vehicle, even tell if he has insurance and what the number is on the decal on his yearly sticker. I only assumed FAA was going to do the same after making the change to put numbers on the outside.
It seems unlikely that there is no one at the FAA who can search their own database. I'd first suspect that you simply asked someone who did not have an answer. Did he try calling HQ to find out?