Your Greenheart was one of the latest ones made by this Zella-Mehlis consortium, as their serial numbers only ran into the 6400 range evidently. HOWEVER, the assembler for this group (Hermann Weihrauch) continued to produce some after the other members of the group left this project and went on to RWM contract production of other arms and materials (around the end of 1935). Weihrauch began marking the receiver tops with their own logo, and shifted the serial numbering up to about 20,000 to produce another two thousand or so.
The very first of these (and only very few) may have been assembled at Venus Waffenwerke, prior to that role being assigned to Weihrauch. Venus made the butt plates, trigger guards, and some other small parts for these, and the company's owner/director Wilhelm Foss was the leader of the Greenheart consortium who signed the group's contract with Mauser for manufacturing rights for the DSM. As with the DSMs from the consortium in Suhl, Greenheart DSMs show barrel signatures showing that a number of participants contributed some work to components supply for these trainers. There were notably fewer consortium players involved in Zella-Mehlis, however.
Hope this helps you out.
Steve