I’ve identified SIX distinct Paul Thompson stamps ranging from around 1905 into the 20’s. It’s not an exact science but in general the photos themselves AND the stamps started small and increased in size over time. By the 1920’s full size 8x10’s were more common with the largest PT back stamps.
The early, small PT stamps don’t seem turn up on the later larger photos. With some research I’m sure the chronology of all six stamps can be figured out to some degree.
Aaron Ward 8x10, 1920:
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