Thanks for the lock. I'm not quite sure what to do with it, but I'm guessing that the firm you are looking for had some connection to Erdmann & Rossi, either through merger, location, and/or personnel. Like Erdmann & Rossi, Karosserie Friedrich Rometsch was located in Berlin-Halensee, and the designer Johannes Beeskow worked for both (I don't know that he ever had his own company). So, is the coachbuilder that you are looking for Karosserie Friedrich Rometsch?