This is not my collecting area, and I'm not a native German speaker, so take this with a grain of salt.
These stamps can be found with three different watermarks (in Michel, Wz 1, Wz 3X, and Wz 3Y). Wz 3X is typically the most common, with some Wz 1 and some Wz 3Y (3Y is the 3X watermark reversed). The design of the three watermarks is referred to as a "Kreuzblumen" (singular, Wz 1) or "Kreuzblüten" (plural, Wz 3X and 3Y), meaning milkwort flower. You can see examples on my website
here.

I believe the notations on all three are references to the watermarks being Wz 1 instead of Wz 3. In short, check your watermarks.