Whatever the reason, the circle is definitely post-mint damage. The mintmark is slightly tilted CCW and a bit close to the date but, not extreme enough to create a premium value. Even if it were, the damage removes any of that potential value.
Keep searching!
Keep searching!

In Memory of Crazyb0 12-26-1951 to 7-27-2020
In Memory of Tootallious 3-31-1964 to 4-15-2020
Oh that I was where I would be,
Then I would be where I am not,
Here I am where I must be,
Go where I would, I can not.
In Memory of Tootallious 3-31-1964 to 4-15-2020
Oh that I was where I would be,
Then I would be where I am not,
Here I am where I must be,
Go where I would, I can not.