This stamp is consistent with the clear impression of the 1E1 printing and the 1E1 watermark, with a notable exception: these stamps were used in 1939 and 1940 and the paper is bright white. The 1E1 paper is cream. My educated guess is that a different pulp was used.
Here is a scan of the watermark.
Here is a specimen postmarked in May 1939.
This specimen has gaps in the overprint.
This specimen has the 2 of 25 deformed. To date, I have not confirmed this flaw as a repeatable plate variety.