Lincoln Wheat cent 1955 D DDO [solved]

Is the coin in the attached photos considered a DDO? Is it worth having the coin graded if it is a DDO?

19mm, 3.11 grams

If it were a 1955 DDO it would be worth having it graded but it's not. Here's one:

There's none reported for 1955D. I believe you may have a repunched mint mark.

https://www.error-ref.com/repunched-mintmark/

TIL: Mintmarks were put into the master die in 1989 in the US.  So before that, was it part of the process directly after the strike?  Or was it a separate machine?

At the time mint marks were added to the finished dies by hand stamping onto the die. That's why exact location can vary and so not considered a variety.  Also, that's why a DDO can be discounted on these coins if the mint mark is doubled.  Notice how all the lettering on this coin is doubled except the mint mark.