Got this coin back the other day. I've had it in my collection for around 25 years and finally decided to verify what I believed it to be and it came back what I thought it was. After years of people telling me it was heat damage I feel a little vindicated that it was a gas inclusion. I just wonder how this would get out for circulation to begin with. The only thing I can figure is that because it was a defective planchet it was kicked out of the stamping process but then at some point someone just pilled it in with the finished product.
