(1) When purchasing only a portion of a member's eligible military, federal volunteer, refunded, Montana public service, or other full-time public service, the member must first purchase the most recent service.

(2) A member who has refunded service more than once must purchase the most recent refund first.

(3) When purchasing or transferring a portion of a member's service credit from another retirement system, the member must first purchase the most recent service.

(4) When purchasing a portion of a member's retroactive service, the member must first purchase the most recent retroactive service.