Employees of the Oklahoma State University Cooperative Extension Service who are members of the Oklahoma Public Employees Retirement System shall cease accruing benefits in the Oklahoma Public Employees Retirement System and shall commence accruing benefits under the Teachers' Retirement System of Oklahoma on July 1, 1987. On January 1, 1988, the Oklahoma Public Employees Retirement System shall transfer to the Teachers' Retirement System of Oklahoma the actual amount contributed to the Oklahoma Public Employees Retirement System by the state and by each employee of the Oklahoma State University Cooperative Extension Service transferring to the Teachers' Retirement System of Oklahoma and the retirement records of those transferring employees. Service accrued by said employee of the Oklahoma State University Cooperative Extension Service under the Oklahoma Public Employees Retirement System shall be treated as credited service under the Teachers' Retirement System of Oklahoma. For purposes of this section, creditable service transferred from the Oklahoma Public Employees Retirement System shall include service authorized under paragraph (f) of subsection (2) of Section 913 of Title 74 of the Oklahoma Statutes. Members who retire prior to July 1, 1990, shall have their monthly benefit adjusted to include all services accrued under paragraph (f) of subsection (2) of Section 913 of Title 74 of the Oklahoma Statutes. Provided however, that any adjustment of existing retirement benefits caused by reason of inclusion of such service authorized under paragraph (f) of subsection (2) of Section 913 of Title 74 of the Oklahoma Statutes shall not affect any retirement benefit paid prior to July 1, 1990.