When the mint mark is in different locations, then you know you have two different dies. (Pre 1990 coins)
If you find two coin mint mark locations the same in an original OBW roll, then you can check markers to see if you have two examples of the same die pair of that run. (Pre 1990 coins)
On the post 1990 coins, the mint marks will all be in the same location on each coin regardless of dies as the mint mark is on the design of that mint.
Edited by coop
03/16/2019 12:55 pm