Agreed.
These are the unit and individual code letters, not the serial number ( which would be Werke Nummer in the Luftwaffe, for example W.Nr. 294732 ), and it is the latter that identifies an individual airframe, not the code letters.
The "G9" designates the Geschwader, with the "DZ" being the Staffel and individual aircraft letters. These could, and would, be carried by a number of aircraft - for example, if "DZ" was lost on operations or damaged beyond repair, then a replacement would receive the same codes. When aircraft types were replaced by the next in the production series, then again the codes would be used. There would not, however, be more than one aircraft with exactly the same codes.
So it can be seen that a number of airframes, over time, would carry the same codes, just as they did in the RAF and USAAF.