(a) Any member of the retirement system who has previously been employed in public employment in any other state of the United States is entitled to receive credited service for the time of public employment in that state, not to exceed five years, if the member substantiates by appropriate documentation or evidence his or her public employment in another state and makes contributions as required: Provided, That the member is not entitled to receive the credited service if the employee is vested or entitled to be vested in a retirement system of the state in which the employment credit was earned and the member is entitled to service credit in that retirement system for the employment period for which the applicant seeks credited service in West Virginia: Provided, however, That the service credit from the other state may not be used to meet West Virginia's eligibility requirements for retirement or vesting.
Members entitled to out-of-state service credit under the provisions of this section shall make additional contribution to the retirement system equal to the actuarial equivalent of the amount which would have been contributed, together with earnings thereon, by the member and the employer, had the member been covered during the period of the retroactive service credit.
(b) In any case of doubt as to the period of service to be credited a member under the provisions of this section, the board of Trustees has the final power to determine this period.