Thanks for the info -makescents-. It is always nice to learn something new here. PIDT, that's a mouthful.
I suspected some sort of die event due to the nearly uncirculated condition of the coin. That pretty much ruled out any PMD
. It seems this particular event might be more difficult to notice on well circulated coins.
Can this be a result of excessive pressure during the strike?
I can remember "ghost image" much more easily and is usually what I use when searching for the PIDT.
I have noticed that it is usually high AU or BU, REDs, that this can be seen on the best. I don't think it has anything to do with an excessive strike but more to do with just another form of deterioration of the dies. I have also noticed, this is more common in 40 series coins. Possibly a weakness in the particular design used at the time or just simply, over-used dies.
Hope this helps some, I'm learning right along with you.