I've seen these marks on virtually all denominations and still can't puzzle out how they form. My current guess is that when the coins are bagged after minting, a couple stack near the bottom of the bag and the reeding from one leaves this impression upon another due to the pressure of the other coins above it. To clarify, I'm not talking about reeding marks in general, but the positioning of them on the inside rim of a coin, as in this dime.
It's because the coin has been struck slightly off center. Look at the width of the rim on the right, compare that to the width of the rim on the left. The partial reeding marks you are seeing are where they should have been and they are formed at the very beginning of the strike. But as the dies come completely together within the collar the planchet is forced to one side or the other by the misaligned dies and the final reeding is then formed on the coin resulting in one side have a much wider rim than the other side.
