A member is entitled to service credit:
(1) for service as a member;
(2) regained under § 27-302 of this subtitle by a member who redeposits accumulated contributions previously withdrawn;
(3) for prior service as provided in § 27-303 of this subtitle;
(4) for military service as provided in Title 38 of this article; or
(5) purchased under § 27-304 of this subtitle.