Any member who elected to contribute on $7,800 prior to January 1, 1978, whose salary was more than $7,800 during the school years 1974-75 through 1978-79, may elect to make back contributions on the difference between $7,800 and the member's actual salary, not to exceed $10,000 for each applicable school year, plus interest compounded annually at ten percent (10%) per annum. Such payment shall be made prior to the official retirement date of the member.
Okla. Admin. Code § 715:10-5-8