Notwithstanding any provision to the contrary, employees of Washington State University who first established membership in the public employees' retirement system plan 1 under *RCW
41.40.500 through
41.40.507, as existing on July 28, 1991, and **RCW
41.40.508, as existing on June 7, 1990, may purchase, as set forth under RCW
41.50.165, plan 1 service credit for the period of service at Washington State University prior to his or her contributory membership in the Washington State University retirement system.