Except as provided in § 22-203 of this subtitle, an individual described in § 22-201(a) of this subtitle who was a member of the Employees’ Retirement System on or before December 31, 1979, became a member of the Employees’ Retirement System as a condition of employment. Except as provided in former Article 73B, § 2-206 of the Code, an individual who is not a member of the Employees’ Retirement System on December 31, 1979, is not eligible for membership in the Employees’ Retirement System.