In addition to the increase in the service retirement allowance for members of the State Retirement System who retired prior to July 1, 1972, provided in Section 9-1-1760 and Section 9-1-1765, all such members shall receive an additional increase in their service retirement allowance of five percent per year computed and commencing on and including January 1, 1978.
S.C. Code § 9-1-1766