The 'waterwheel' stamps of Bavaria
The first postage stamp of Bavaria was issued on November 1, 1849. This square stamp in black was designed by Peter Hasseney and engraved by Franz Max Josef Seitz. The stamp had a value of 1 Kreuzer. They were printed at the University Printing Office in Munich. Later, other values in the same design followed: 3 Kreuzer, 6 Kreuzer, 9 Kreuzer, 12 Kreuzer, and 18 Kreuzer.
Later, all values followed in changed colors. The stamps were postmarked on the letters with a place name stamp. This took place from November 1, 1849, to July 31, 1850.

Subsequently, new stamps were introduced in the shape of a waterwheel containing only a number. This number corresponded to a specific post office. A whole list of numbers was created from August 1, 1850, to November 20, 1856, from number 1 to number 603.
However, in November 1856, the Bavarian PTT decided to recall all number stamps to redistribute them. The first alphabetical order had become severely disrupted by the ever-increasing number of post offices; consequently, a new alphabetical list was created, to which three more offices were added. The new distribution was implemented from December 1, 1856, to March 9, 1869. During the period when the number stamps were unavailable, from November 21 to November 30, the place name stamp was again used to stamp the stamps. The series of numbers ran from number 1 to number 606.
In the period from December 1, 1856, to March 9, 1869, 185 replacement stamps were supplied to offices that had returned the stamp due to wear and tear, for example. However, the model of the waterwheel stamp modified. In collecting circles, the first model is called the closed waterwheel stamp. This is because the new model had become an open waterwheel.
But even more happened during that period. A total of 315 more offices were added, expanding the series from number 607 up to and including number 922. These stamps were manufactured in the new, open waterwheel model. Numbers 921 and 922 were no longer put into use, leaving a total of 920 numbers. Many collectors consider it a sport to match all the numbers and the corresponding name of the office where the stamps were used. A list of numbers and office names can be found in the book 'The mill wheel stamps of Bavaria', written by Erich Stenger in 1915. This book is still considered the standard work in that field. It is just a pity that the numbers of a great many stamp impressions are not recognizable.
If you enjoy puzzles and like using stamps, this is a great opportunity! Do you enjoy puzzles too? You might well come across the rarest impressions: numbers 35, 894, 899, 905, and 908 through 920. All stamp impressions are in black ink, but there are also impressions in blue, which are very rare. And the red color only appears on numbers 345 and 370. Super rare. Good luck!!
That puzzle enthusiast must have a very fat wallet to have those stamps in their own collection. I’ll piece them together myself using the prints in the catalogues of the various national and international auctions. That’ll keep me busy for a while!
I have a piece of postal stationery that appears to have been used and is stamped with a closed waterwheel stamp. The item is also stamped: GB WERBESCHAU 30.6.7-8N München 1912.
The water wheel is 16 mm in diameter instead of the old stamp of 19 mm.
Was the stamp reused in 1912 or is it a forgery? The stamp bears the number 51.
Jacques, number 51 belonged to the DEINING office during the first distribution. It was in use from August 1, 1850, to November 20, 1852. Upon the redistribution, number 51 was assigned to the BOBINGEN office. This office used the stamp from December 1, 1856, to March 9, 1869. After that, the stamp was withdrawn and no longer used. Naturally, I cannot determine from your description whether the stamp is 'genuine' or a 'forgery'. But in any case, it is not an impression of the original stamp.