Question about a filled in D

This is a 1987- d and a 1979-d cent, the d is filled in, is that a error????

 

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I sorry 1978-d and 1979-d

 

It is a common error in coin before 1985. In 1985 the

mint marks D , P , S were enlarged.

 

Filled mint marks are very common. They can be the result of many things, including grease or other foreign substances in the die at the time of strike, die wear, or even circulation wear which has lowered the high point of the mark.

 

Very common. Usually caused by a die chip or die wear.