1891 10c red, tied to piece by "San Sebastián" cds in September 1891. In addition to four covers, the only piece known used with this cancellation. Illustrated by Brian Moorhouse in his handbook on page 52, and described as: "This piece was illustrated by Eugene Klein in s short article in the 'Collectors Club Philatelist' Vol. XI No. 3 of July 1932 (...). The date would appear to be '9 SE 91' with just a two letter month abbreviation. If this date is accurate then this would make it the latest recorded use of a Popper stamp", ex Worthington. (Image)