I was in the military (enlisted service) from 1972-1975 and again (officer service) from 1979-2006. Can you explain how Deemed Military Credits (DMC's) work and how do I verify that SSA has credited me properly?
Deemed military wages are extra wages that Social Security adds for periods of active U.S. military service (https://www.ssa.gov/OP_Home/handbook/handbook.09/handbook-0953.html). For the period 1957-1977, an extra $300 in wages is granted for each calendar quarter in which a person had active duty. From 1978-2001, the extra amount is $100 for each month in which a person was on active duty. These extra wages are then added to the rest of the veteran's Social Security covered earnings when calculating their retirement benefit rate. The normal computation method is used (https://www.ssa.gov/pubs/EN-05-10070.pdf), except that up to an extra $1200 in deemed wages is added for years in which a person was on active duty in the US military.
Starting with 1968, Social Security began crediting these deemed military wages automatically. If you compare your W-2 forms in the years that you had active military service with your Social Security earnings history, you should see that the credited amount is higher than the actual W-2 earnings on which you paid Social Security taxes. I can assure you based on my long career with Social Security that the process of crediting deemed military wages starting with 1968 is virtually foolproof, so you needn't be concerned about receiving the proper credits.