Probably some chatter in the chamber, die deterioration. This year was struck well overall with the exception of the "S" which, along with all the other "S" mintmarks from 1968-1974 were sloppy.
Die Deterioration Doubling,Die: Deterioration doubling (DDD) is a common form of mint-made error on many United States and Canadian coins that results from degradation of the die used to strike the coin. Due to a combination of improper preparation and treatment of the dies, excessive wear, and overuse, die deterioration doubling has occurred on nearly every series issued by the US mint in recent times
It's not flat or shelf like. It's not on any other sides. Must've been last day for that die. Thanks.
