(1) Beginning with retirement allowance payments due on or after June 1, 2004, retirement allowances granted under section 27 that began before the effective date of the amendatory act that added this section shall be adjusted as provided in this section.

    (2) Except as otherwise provided in this section, a retirement allowance shall not be less than $6,000.00 per year.

    (3) A portion of a retirement allowance payable to a surviving child or parent shall not be less than that portion of a retirement allowance that the child or parent was entitled to receive under section 27 before the effective date of the amendatory act that added this section.