P1 is a very common stamp. Value is in the $1-1.50
The Double overprint (P1a) is rare and lists at $3,000 M and $4,000 MNH, last time I looked. Not sure if it changed much in the 2020 catalog. If you saw a double overprint priced at $1, go for it, even if it is a counterfeit, it probably is worth it.
rrr...
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