Simple: The German Deutsches Reichs Patent Law became effective in 1876 only. Before, patents or privileges were a matter of the many independent German states like Prussia, Bavaria, Saxony, Wuertemberg, Baden, Brunswick and many even smaller ones. All had their own patent laws, habits and archiving. Probably there never was any patent for the pre-1870 designs by Nikolaus or Franz von Dreyse. Soemmerda and the Dreyses were in Prussia. Prussia as a rule never patented anything that might be of military importance to the realm.