Help me with this coin!!!

Dron

Back in 1999 I ordered 9pc proof set. When I opened it up, on the back of one of the sets, a lincoln peney looked like the paint was kind of smushed around on a reverse. And still till today there is a big yellow or orange spot on there but you can still clearly see the coin. I am gessing that it hapend during the last process of proof making coins.
Any Ideas???

FC57Coins

could be some sort of glue from the process of putting the sets together - either way if it's a foreign substance, and it has adhered to the coin, the coin is worthless, although I can't imagine that cent being worth all that much and it's replaceable.

Frank