(1) At the time of a member's application for retirement, the department does not have all information necessary to make a final computation of the member's retirement allowance. The department shall compute an interim retirement allowance that shall be paid to the member until the department's final computation of the member's retirement allowance. The interim retirement allowance is an initial, estimated computation of the retiree's retirement allowance subject to adjustment by the department based upon subsequent review of information provided by the member's employer.

(2) In computing the interim retirement allowance, the department may, subject to later correction, consider only the amount of the member's salary actually reported by the employer up to the date of the interim computation, but may impute the member's earned service credit for the same period.

(3) Every employer of a member who applies for retirement shall provide the department with a final compensation report for that member. The report shall be completed on a form provided or approved by the department.

(4) Following the department's computation of the interim benefit and receipt of the employer final compensation report, earnings history, and any additional information requested by the department, the department will complete a final computation of the member's retirement allowance. The department's final computation may increase, decrease, or leave unchanged the amount of the interim retirement allowance computed pursuant to subsection (1) of this section.

(5) Pursuant to RCW 41.50.130, either before or after the department's final computation of the member's retirement allowance as provided in subsection (4) of this section, the department may adjust a member's retirement allowance to correct any error in retirement system records. For purposes of this subsection, errors in retirement system records include, but are not limited to, the following:

(a) Applying an incorrect retirement allowance formula in computing the retirement allowance;

(b) Including service that is not creditable to the member;

(c) Including payments that do not constitute basic salary to a member in the member's retirement allowance computation, or excluding basic salary not reported by an employer;

(d) Benefit overpayments and underpayments;

(e) Including an individual in the membership of the retirement system or plan who is not entitled to such membership;

(f) Excluding an individual from membership in the retirement system or plan who is entitled to such membership.