A 1901 2c Pan-American centre invert was the leading lot across four sessions of sales at Kelleher Auctions between September 18 and 19.

One of just 200 printed, and one of only seven known used examples, the stamp sold for $38,350 at the Flagship Series sale in New York.

One of just seven used examples thought to exist

It wasn't just its scarcity that made the stamp desirable to collectors.

The auction house explains that it is an "impressive well centered example of this extraordinarily rare used inverted center, with this being among the best centered of that tiny group".

With around 150 extant, unused examples regularly cross the block, states the auction house. Examples of the seven used stamps auction far less frequently.

Only slight creasing, a tear at the bottom, and reporforating at the top stopped the 1901, 2c from getting closer to its $60,000 Scott catalogue valuation.

Six stamps were created to commemorate the 1901 Pan-American Exposition in Buffalo, all displaying America's mechanical prowess. The two-colour design on the 1, 2 and 4 cent stamps saw several sheets printed with an inverted central vignette.

A 1909 4c orange brown on bluish paper provided the second highest lot of the sales. It sold for $21,240, a testament to its scarcity - less than 100 are known - its superb colour and its "fine to very fine" condition.

There was also a strong showing from a complete matched set plate block of six 1930 Graf Zeppelins.

Benefitting from their never hinged status, and "post office fresh condition", the lot made $18,850.

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