Memory detail fades a little after the years, I'm afraid ...
Was attending a course of some sort (probably engineering or FT related) and the presenter's discussion got onto a well-known older pilot of note (a very senior OEM design engineer as I recall) who owned and flew an equally old aeroplane of equally well-known note.
Apparently, in discussion, the older pilot had observed that his aeroplane wasn't registered. When one of the folks in the discussion commented that such could affect his pilot licence, he observed that he had never had one of those ....
Much chuckling around by the assembled folks. Guess I'm not too sure just what the outcome may have been had the Gestapo requested he produce one or the other ...