Ave - I was hoping someone more knowledgable than I would answer you excellent question, which is a bit more complicated that it appears on the surface.
Between the factories of RWS Nürnberg and the GECO factory at Durlach, there was for years the incorrect belief that each made all their “own” ammo; by “own” I mean that RWS made “RWS” headstamped cartridges and GECO made “GECO” headstamps cartridges. Since, information has been readily available concerning a working agreement between the two companies, dating from c.1927, whereby RWS was to make all the rifle ammunition and Geco all the pistol ammunition, for both companies brand names. We know that to be basically true afer that time concerning commercial ammunition.
Military contracts often contain much more stringent requirements than commercial production requires. As you point out, we know that the code dnh was assigned to the Durlach Factory, and cartridges using that manufacturer’s code were made there, by Geco. It is a fair assumption that the commercial or police-style contract headstamps using the factory initials RWS in a quasi-military style headstamp (usually dated, and sometimes with an additional number that could possibly be a month rather than a lot number - I simply have never been sure of that) were actually made at Durlach also.
However, there is no question that RWS Nürnberg also made pistol ammo, at least the 9 mm 08 cartridge, as we have cartridges from the 3rd Reich era with both P151 and dnf headstamps, both codes assigned to RWS Nürnberg. That leaves open a slight possibility that the so-called police-style headstamped 9 mm contracts were made at Nürnberg as well, although like you, from the font, and features, I suspect most if not all were made at Durlach.
Even as regards the Nürnberg factories, there is is confusion, because RWS operated two factories there, one being the old Utendõrfer factory in downtown Nürnberg, and the other was at Staldeln. Both used the “dnf” headstamp code. In the case of 7.9 x 57 mm ammunition, case-lots 1 thru 49 were assigned to the downtown factory, and lots 50 and up to Stadeln. I have no clue as to whether or not this pertained to 9 mm 08 cartridges or not. I do not collect lot numbers to even know if there were any 9 mm case-lots over 49 on that caliber or not, and I do not have Lew Curtis’ book handy at the moment to check it out.
I think this was the only instance of one company using the same manufacturer’s code on products from two different factories, during the life of the German letter-code system. Certainly it was in regard to production of cartridge cases for small-arms ammunition.
In the long shot, though, I believe that the “RWS” headstamped 9 mm and that with P405 code using the same font and with the same general characteristics, were likely made at the GECO factory at Durlach.
Again, I could be wrong on that final conclusion, and would welcome someone like Lew, Morten, or Dutch chiming in here. I am a total amateur compared to those guys.