I was going through the US Air Mail section of an old Minkus album and came across a blank space for a stamp that I did not recognize.
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The stamp commemorates the 11th Inter American Conference in Quito Ecuador in February 1960. According to a couple of Linn's articles, the stamp was designed, announced, and plates were created (Pl# 26564-26567), but the conference was postponed, then postponed again. By the time the conference was held, in March 1961, the postage rate was close to being changed from 10c to 13c, so the plates were destroyed and the stamps never printed.
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"Something over 300,000 first day cover requests, which had piled up at City Post Office in Washington since the stamp was first announced on October 2, 1959, are being returned to the senders."
https://www.linns.com/news/us-stamp...at-never-washttps://www.linns.com/news/us-stamp...hy-it-wasn-t