I can add a little info.
Baujahr refers to the year of manufacture and German manufacturers were required to stamp this on all bikes sold in Germany but they seemed a lot more relaxed about doing it on export models. Yours in not the first bike I've come across with the final year stamp missing. You know it was at least made in the 1950's.
Hubraum refers to the capacity of the engine and your plate identifies it as a 250, not a 150.
Hope this little bit helps.
Cheers,