20c Special Delivery
The different OB positions would indicate that a single hand pressed OB device was used. 

Double OB

Plate Block of 6

LARGEST RECORDED MULTIPLE

Listed as only 9 produced and apparently this is erroneous. The above 4 singles and block of 6 verified as Scott #E2, watermarked double-lined USPS. Including the above, my current tally is at 21 stamps with the other eleven consisting of a B/4, a pair and 5 singles.

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