Has what appears to be an upside down P after unum and a lamentation or die break under Liberty's chin.
some folks think these extra letters on the edge of the new dollars come from the ejection system of the edge lettering machine. I don't know if they will be worth very much but I keep everyone I find. I now have over 200 of them with some having 3 or more extra letters.
Rick a lot of folks including me think the incuse letters from the coins got pushed into other coins from a pile up in the edge lettering machine.I'm thinking the coins entering the edge lettering machine were used to push the finished coins out of the machine. I believe the inverted letters on the coins edge worked like a die and created raised letters on other coins.
I believe you are right about these not being called a mint error because even if it happened at the mint the coins had already been struck.