Okla. Admin. Code § 715:10-5-17
All credit for active military duty performed after July 1, 1943, must be purchased prior to the official retirement date of the member. No credit or adjustment will be made to a member's account after retirement unless evidence points to a clear and convincing error on the part of TRS staff. The Executive Director will rule on the circumstances when such cases arise. Credit for active military duty will be accepted for eligible service prior to July 1, 1943, when evidence of such service is provided to TRS. An adjustment in the monthly retirement benefits of the member will be made beginning with the next check due if proper documentation is received by TRS by the 15th of the month. The adjustment in benefits shall not be retroactive.
Okla. Admin. Code § 715:10-5-17