I was checking the reverse sides of all my proof sets for the "FG" in halves, when I came upon this. The coin is still in it's original packaging (unopened) & I've been in possession of the set since it's shipment from the mint, so I'm relatively certain these are not PMD. I forgot to note the year & I keep all coins coins offsite, so if there are any questions regarding the year, give me a day (2 days if on weekend) to retrieve it.
Spots you see are not quite pits, yet; they are toning spots. It’s hard to say why this happens. Sometimes coins are stored where the temperature goes up and down constantly. That promotes condensation in the holder which promotes spots. Sometimes the mint does not rise their planchets property before they strike the coins. Sometimes the packaging that holds the coins is not inert and promotes toning. At this point there is nothing you can do. You can deep the set or buy a replacement. At any I would re-think you storage location. It might no be the best place for coins.
I do not see any pitting (fortunately). That would be actual holes in the surface of the coin, which fortunately you do not have. These are more commonly referred to as "milk spots", which is still a minor negative, but not as bad as pitting would be. So you've got some milk spots and haze happening there- both common problems with proof coins- but they're not horrible. They essentially make this an average quality coin rather than a high quality one. Edit to add: if this coin were actually pitted, the pits would look like those craters on the moon. As to the year on the coin, you don't need to tell us. That's a Bicentennial issue from 1976. It's the only year they used that design with the Liberty Bell on the reverse. There are varieties in the Bicentennial Ike dollars- a Type 1 and Type 2 reverse, if I remember correctly. It has something to do with the "fatness" of the lettering on the reverse, I think, but I will let the others tell you more about that since I don't really do much with modern US coins.
