It is fairly easy to distinguish stamps printed by the wet printing method from those printed by the dry method.

The paper used to print the Admirals was machine-made wove paper. The stamps were printed on the paper so that the grain of the paper was vertical. When the stamps from the wet printing shrank, they shrank across the grain of the paper and became narrower. Stamps printed by the dry printing method did not shrink because the paper was not dampened.
Both stamps in the illustration above are the same height, but the wet-printed stamp is narrower by about half a millimeter.

An easy way to determine whether an Admiral stamp is printed by the wet or dry printing method is to lay one stamp on top of another. Notice on the illustration above that the stamp on top is narrower than the stamp it is partially covering.
https://bnaps.org/ore/VanSomeren-Ad...Printing.htm