If that were an American coat, I'd put it much earlier - aughts to early 20s - based on the label style and the buttons. It's possible German tailors were slow to evolve on those points and it could be later. Especially since the morning coat (Frack in German) is a more formal garment. Formal clothes tended to evolve the slowest. Still, I'd put it in the earlier part of your range and would not rule out pre-30s if that's a possibility based on what you know of the tailors.