In the 50s and 60s volunteers had a serial number starting with "RA" for Regular Army. I can't remember what drraftees, guard and reservists used.
In the 70s they switched to using your Social Security Number for your serial number. For a couple of years while te transition was made most had two serial numbers.
So9
.....Westy....
The DD Form 214 which we were all advised to register at the local courthouse upon retirement is, as a public record, now being retrieved by identity thieves who use its information which conveniently includes the retiree's SSN.