(a) As soon as practicable after a member files a statement of prior service under Section 853.103, the municipality that employs the person who receives the statement shall verify the prior service claimed and certify to the board of trustees the amount of service approved and the member's average prior service compensation.
(b) The average prior service compensation of a member is computed as the average monthly compensation for service performed for a participating department of the municipality:
(1) for the 36 months immediately preceding the effective date of the department's participation in the retirement system; or
(2) if the member did not perform service in each of the 36 months immediately preceding participation, for the number of months of service within the 36-month period.
(c) The board of trustees may adopt rules concerning verification and certification of service and compensation under this section.