S.C. Code § 9-1-820
Subject to the restrictions herein contained and to such other rules and regulations as the Board may adopt, the Board verified or, if such verifications have not been completed, shall verify, as soon as practicable after the filing of such statements under Section 9-1-810, the service therein claimed. In lieu of a determination of the actual compensation of a member that was received during such period of prior service the Board may use for the purpose of the System the compensation rates which, if they had progressed with the rates of salary increase shown in the tables as prescribed in 9-1-250, would have resulted in the same average earnable compensation of the member for five years immediately preceding July 1, 1945 as the records show the member actually received.
S.C. Code § 9-1-820