Liberation stamp 1945
The answer to prize question 6 is clear if you turn the image of that faint impression over and compare it with the stamps from 1945, the Liberation Stamp NVPH 443. This stamp was issued earlier. The 1945 proof was probably applied to a piece of paper that later proved to be usable for the 1946 proof. The mark is a so-called clipping mark, applied by the Stamp Values Service before the proof paper went to the printer (control mark).
Thanks to Cees Janssen for the puzzle and images. 
Hello, I have 2 liberation stamps, one with a soldier on it. Is it worth anything? I can't find it anywhere.
Greetings