US #2521a Make Up Rate - 1991 Imperforate Vertical Pair

It's rare to find fully imperforate commemorative stamps, especially among modern issues when technology was supposed to prevent printing errors. However, a few sheets of this 1981 'Make Up Rate' vertical imperforated pair issue were discovered, and you can add this rarely-seen error to your collection at a very affordable price. (United States #2521A)