To the delight of many collectors, in 2012 the US Postal Service began to release new issues as uncut press sheets without die cuts. These so-called "Modern Imperfs" were a staple philatelic product until late 2016, when they were suddenly discontinued. Luckily, these collectible stamps reappeared in 2021, with almost every commemorative issue that year having an imperforate counterpart. Many of these modern imperfs are scarce. If we are able to offer a complete year set, including every imperforate stamp issued in a given year, the year set is followed by "IA," for example “YS2015IA.” Short sets, which are missing some of the scarcer imperfs, are designated with an "I," for example “YS2021I.”