One more piece of information. Mint Marks are not Doubled. You can't use the word Doubled for it.. So that is not what you think it could be. I'm Thinking just DDD - Die Deterioration doubling. But that is worthless doubling which has nothing to do with a true Doubled Die variety.
When you see doubling on the mm and all the devices especially a zlincoln you can 99.9% of the time put it in the worthless doubling category.