Wash. Rev. Code § 2.12.045
(2) Notwithstanding any provision of law to the contrary, effective July 1, 1979, the monthly benefit of each person who either is receiving benefits pursuant to RCW 2.12.020 or 2.12.030 as of December 31, 1978, or commenced receiving a monthly benefit under this chapter as of a date no later than July 1, 1974, shall be permanently increased by a post-retirement adjustment. This adjustment shall be in lieu of any adjustments provided under RCW 2.12.037 as of July 1, 1979, or July 1, 1980, for the affected persons. Such adjustment shall be calculated as follows:
[ 1979 ex.s. c 96 s 4.]