Here’s the little F-er: http://www.loc.gov/item/dcmflute.0465
They actually don’t seem to have a real Eb (Db) CAZ piccolo! At least, my searches aren’t finding one.
The registered number is probably something to do with Department of Trade or MoD (War Office back then?) licencing or design or patent type registration. It clearly isn’t unique to the individual instrument and is not the serial number. I suppose that would bear further research to clarify…