5 CFR §839.902

1. (a)If your qualifying retirement coverage error was not previously corrected, the amount erroneously withheld for CSRS retirement deductions will be:
   1. (1)Used to pay your new retirement deduction amount; and
   2. (2)Applied toward any Social Security taxes you owe for the time you were in the wrong retirement plan.
2. (b)You will get Social Security credit for all the time you were erroneously covered by CSRS. Your employer will send the Social Security Administration a record of your earnings for all the years you should have had Social Security coverage.