Hi! I had these 4 graded in 2020. Anacs labeled them as "circle die mark under lip" and noted that "the exact cause of this is unknown and is under investigation". Here I am, 3 years later and I think I finally have an answer!! Rockwell hardness test? I found some images online of other coins with the error and some of them match my Quarters to the T! (I'll include an image of a penny with the error that I found online) So far, I have 4,another man has 3 or 4 and another man has 1 so under 10 known. All in the same spot on the 2019 W San Antonio.
My question..is this really considered "rare to extremely rare" and since they're on a W quarter, that should raise the value correct? If you don't believe that this a "Rockwell hardness test", do u have any idea as to what it could be? Thank you all for your time:-)