It is possible it is a "Struck-thru debris" which is a genuine mint error, not worth but a buck or so, no big deal. I'm troubled by the shape and inner "layer" for lack of better word/description. The inside ring and discoloration seems to be melted. Possibly by a soldering iron, that would pass the threshold melting point of cupronickel. My opinion is for the latter. If it had been a flame(lighter) more discoloration and a risen outside would be seen, not so w/hot metal tip. I'll have to try this some time...



























