A 1901 2c Pan-American mint invert was among the highlights of Kelleher Auctions' Flagship US, British and Worldwide Stamps and Postal History sale.
The lot crossed the block in New York on February 4, achieving $29,500.
The 2c Pan-American invert was printed accidently and sent out to US post offices
It's one of a series of stamps showcasing American technological advances released for the 1901 Pan-American exposition.
Due to the complexities involved in the two-stage printing process, three values in the series were issued with at least a couple of inverted sheets.
The 1c and 2c issues were accidents and were sent out to post offices. The 4c invert was printed as the result of a misunderstanding.
Around 150 examples of the 2c are known to exist.
In 2013, Kelleher sold a considerably rarer used 2c invert for $38,350.
A block of 10 unissued 1998 "H" Hat error stamps also performed well, achieving $12,980.
The stamp, set at a proposed new postcard rate, was delivered to post offices prior to a postage rate rise in 1999.
However, as the postcard rate was not changed, the stamps were not needed and were returned - although, as is often the case, a few found their way into the collector's market.
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