My “Top Five” were W. Hagelberg AG, Berlin – Lithographisch-artistische Anstalt Muenchen (vormals Gebr. Obpacher) AG, Munich – Albrecht & Meister AG, Berlin – Berlin-Neuroder Kunstanstalten AG, Berlin/Neurode/Dresden and E. Nister, Nuremberg. All five companies would had been in the position to produce the Winsch-back cards.
The answer was suddenly found quickly. It had been “no. 2”: Gebr. Obpacher, Munich.