Mint Mark on 1980 US Quarters

I have noticed on the 1980 US quarters that all of the Mint Marks are filled in on both the D and the P mint mark. One looks just like a blob not even a mint mark. Has anyone else noticed this?

Thank you.

 

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Very common for that date to have filled mint marks. As well as some other dates in the 80's. The red book list nickels as well as quarters 1979 to have filled S and clear S

 

Thank you so much for your response!

 

Any time you're very welcome