I thank this is a strike though error. My daughter picked up a couple of mixed BU rolls cents from year 58 to 74 she gave too me for Christmas. let me know what you think . Thanks for looking!
Just my amateur opinion. it looks more like a plating ISSUE. See it's going on in spots on his coat/face as well. Awaiting more answers....
I tried to get it in a picture but when you look at it from the side in that area it is in dented and looks polished or more shinier than the rest of the coin
Yes to a struck through grease. The spreading out after the initial splotch shows the grease thinning out. Cool find. Roger is correct, these were not plated but still bronze.