Subject to subsection (c) of this section, as a condition of an individual’s employment contract, an individual may remain a member of the Employees’ Retirement System or the Teachers’ Retirement System without change in the benefits under that retirement system as of December 31, 1979, if: the individual is a member of that retirement system on December 31, 1979; and the individual’s membership does not terminate under § 22-217 of this subtitle. Subject to subsection (c) of this section, an individual receiving benefits under this title on December 31, 1979, shall continue to receive the benefits provided as of December 31, 1979. The benefits that an individual may continue to receive include: eligibility for service retirement on or after 30 years of eligibility service or age 60; eligibility for a reduced service retirement allowance after a certain length of eligibility service; a normal service retirement allowance of one fifty-fifth of average final compensation multiplied by the number of years of creditable service; the retirement allowances provided for ordinary or accidental disability; the selection of options for allowances; the adjustment of the allowance for increases in the Consumer Price Index; the death benefit; the level of member contributions; and the length of eligibility service for members to vest benefits in the system. For a member who receives creditable service under this title on or after July 1, 1984, §§ 22-219 through 22-221 of this subtitle determine: the rate of earnable compensation that is payable as member contributions; the computation of the member’s allowance; and the cost-of-living adjustment of the member’s allowance.