Question about wear and DD

[BC1969]

How does a person tell if a coin is a true double die if the coin is heavily circulated?
Meaning any split serif that may have been present have long since worn away.
I've tried searching for this information, but it eludes me.
I believe this coin could be a DD, due to the extra thickness on the 940, but it is very circulated.



Maybe I'll learn something.

 

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[huntsman53]

Is the coin a Philly or a "D" or "S" Mint? There are no listed DDO's for the 1940-P but there are 4 listed for the 1940-D and 5 for the 1940-S Mercury Dimes. The "0" in the Date has a similar appearance to the 1960-D "Small over Large Date" Lincoln Cent.

 

[BC1969]

Doh!
I didn't realize that I forgot the reverse pic.
San Francisco mint.