Hello,
The Encyclopedia of Spring Air Pistols (John Griffiths) estimates up to 16500 with the highest number at the time of publication being 16492. Apart from the usual small and large frame versions, the book also references the existence of an extended barrel variation thought to be a genuine factory modification. There are no markings on the pistol which may have been an experimental prototype.
Apparently a few, slightly more primitive pistols were produced by F. Jung in 1925, which may have formed the basis for the design eventually produced by Hubertus.
Regards
Brian