Model 31 existed in different versions with two different nib shapes and matching front sections exchangeable among each other; additionally at least two further front-part variants exist. The trailing 'P' stands for 'Patronenfüllhalter' (cartridge pen) and marks the cartridge variant. The variety is considerable, so identical-looking pieces side by side can actually differ. For exact attribution, comparison with specialist literature and the gallery on Fountainpen.de is worthwhile.