Contributory service credited to Board of Regents employees--Eligibility of nonparticipating employees--Qualification for prior credited service

Employees of the Board of Regents shall be credited with contributory service for each year such employee participated in the retirement plan in effect between April 1, 1964, and June 30, 1975. Employees of the Board of Regents who did not participate during all the years that they were eligible to participate in the Board of Regents retirement plan in effect from April 1, 1964, to June 30, 1975, are eligible for credited service only if purchase is made pursuant to §