I bought this 1891-O seated dime a few years ago for about $4.50, which at the time was about 2x melt. For the longest time I have set it aside for more interesting stuff. However, recently, I took another look at it and noticed something on the reverse: Look between 10:00 and 11:30. At first, you may think the missing detail is just wear. However, notice how the lack of detail firmly drops onto the design - it must be a die break. In addition, there is a small die break at 9:00 in the wreath. I looked at the Fortin guide and attributed this coin as F-124a - an R-5 variety. Although there isn’t much of a premium given the low grade, it’s still an interesting find, especially seeing as I’ve never seen any sold online.
Cool coin! On PCGS’s CoinFacts, there’s a picture of one (I believe it’s the same variety) in MS66 where you can see all of the details on the retained cud.
In The Complete Guide to Liberty Seated Dimes (1992), Brian Greer "numerous examples exist with shattered dies, cuds, or massive clashes". He has 5 pictured, but doesn't comment on rarity. One has a cud in the same area as yours, but it isn't a match
