Except as provided in § 22-207 of this subtitle, an individual who was a member of the Teachers’ Retirement System on or before December 31, 1979, became a member of the Teachers’ Retirement System as a condition of employment. Except as provided in former Article 73B, § 3-206 of the Code, an individual who is not a member of the Teachers’ Retirement System on December 31, 1979, is not eligible for membership in the Teachers’ Retirement System.