Eligibility service for a member of the Employees’ Retirement System or the Teachers’ Retirement System consists of service credit: for employment as a member; transferred from a retirement or pension system under Title 37 of this article or Title 31, Subtitle 1 of this article; for military service, as provided in Title 38 of this article; purchased under this subtitle; and that equals, for a member who has transferred between the Employees’ Retirement System and the Teachers’ Retirement System, the member’s eligibility service recognized under the previous system through the date before the member became a member of the current system.