Wash. Rev. Code § 50.29.080
The commissioner may redetermine any contribution rate if, within three years of the rate computation date he or she finds that the rate as originally computed was erroneous.
In the event that the redetermined rate is lower than that originally computed the difference between the amount paid and the amount which should have been paid on the employer's taxable payroll for the rate year involved shall be established as a credit against his or her tax liability; however, if the redetermined rate is higher than that originally computed the difference between the amount paid and the amount which should have been paid on the employer's taxable payroll shall be assessed against the employer as contributions owing for the rate year involved.
The redetermination of an employer's contribution rate shall not affect the contribution rates which have been established for any other employer nor shall such redetermination affect any other computation made pursuant to this title.
The employer shall have the same rights to request review and redetermination as he or she had from his or her original rate determination.
RCW 50.29.080
Effective date-1970 ex.s. c 2: See note following RCW 50.04.020.