While the 1838-O is undoubtedly the rarest date and most famous key of this short-lived type, the 1839 Small Letters issue is the only one to be listed in the Guide Book of United States Coins as "(ex. rare)," a numismatic benediction given to only the most elusive issues. Discovered in 1972, just 10 examples have been located despite the variety's distinctive appearance and the dedicated searching by legions of half dollar specialists. The coin's discovery is recounted in Breen's Complete Encyclopedia. It was acquired by Maurice Rosen while he was briefly Breen's coworker at First Coinvestors, Inc. Breen, given the first chance to study the new variety, recognized that the unusual reverse featured the same eagle hub as the rare 1839-dated Judd-95 pattern, a muling of unrelated dies that was produced by the Mint for collectors in the 1860s. The eagle is described by Graham as "smaller and more compact than any eagle on any other variety." The legend is also "smaller and farther from the rim." The easiest characteristic to see at arm's length is the position of the lowest arrow feather in relation to the olive branch: just the tip of the arrow feather is visible below the branch on this reverse, whereas all other reverses show a substantial proportion of the feather's detail below the branch's end. Untold thousands of times, cherrypickers have turned over an 1839 half dollar hoping to identify a specimen of this rarity, and fewer than 10 times has their coin flip been rewarded.

As a major variety listed in the Guide Book, the 1839 Small Letters variety is the single greatest stumbling block to completion for specialists in the Reeded Edge, Capped Bust half dollar series. While collectors could perhaps escape the necessity of owning an 1838-O by defining their collection as including only coins struck for circulation, there is no avoiding this variety's importance or rarity. Most survivors are well worn or badly impaired.

The example to the left was sold by Stack's Bowers Galleries in the November 2019 Baltimore Auction, where it realized $90,000.