27 Miss. Code. R. 210-08-101
Any former employee with prior service with any department of the State of Mississippi, or any County, Municipality, or any Subdivision or Instrumentality, who, after April 15, 1952, but prior to July 1, 1953, re-enters either the department for which prior service was performed, or any department, county, municipality, or instrumentality covered under the Public Employees' Retirement System and becomes a member of said Retirement System, shall be required to remain in service and contribute to said System for a period not less than four years before his certificate of prior service shall become final except in those cases where persons are prevented from completing the four year requirement because of total and permanent disability or because of having attained the compulsory retirement age of 70 years.
27 Miss. Code. R. 210-08-101