From the first printed stamps in South Korea in 1946 after the WWII, up to around 1953, many of those issues can be found printed as imperforated stamps, double printed stamps and stamps printed on both sides. The stamps were issued by the US Military from 1946-1948. On August 15, 1948, the South Korean government issued its first stamps, independently from the USA. This author, while accumulating a number of these imperfs and errors over many years, has not actively collected these varieties, as he believed there was little documentation of these issues, and no catalogue values to determine the rarity.
Many of these stamps are still available today by collectors in auctions and on-line philatelic website for relatively low prices. After 1953 there are very few imperforated stamps or errors found in South Korea as the security and quality control of the printings must have improved dramatically.