(

a) In addition to the increase in allowance authorized and granted pursuant to

Section 21313, and notwithstanding the limitation on that increase imposed by this

article and subdivision (

b) of

Section or subdivision (

a) of

Section 21337.1, effective January 1, 2000, or the date this

section becomes applicable to the contracting agency, the monthly allowance paid with respect to a state, local, or school member who retired or died prior to January 1, 2000, or the date this

section becomes applicable to the contracting agency, other than an allowance provided by

Article 3 (commencing with

Section 21570) of

Chapter 14, shall be increased by the percentage set forth opposite the year of retirement or death in the following schedule: Period during which retirement or death occurred: Percentage: 24 months ending Dec. 31, 1999 0.0% 12 months ending Dec. 31, 1997 1.0% 24 months ending Dec. 31, 1996 2.0% 60 months ending Dec. 31, 1994 3.0% 60 months ending Dec. 31, 1989 4.0% 120 months ending Dec. 31, 1984 5.0% 12 months ending Dec. 31, 1974 or earlier 6.0% The percentage shall be applied to the allowance payable on January 1, 2000, or the date this

section becomes applicable to the contracting agency, and the allowance as so increased shall be paid for time on and after that date and until the first day of April immediately following the date of application. The base allowance shall be the allowance as increased under this section. Notwithstanding

Section or 21337.1 to the contrary, this increase shall not be included in determining the initial monthly allowance upon which a supplemental benefit is payable pursuant to

Section or 21337.1. (

b) This

section shall not apply to any contracting agency unless and until the agency elects to be subject to its provisions by amendment to its contract, made in the manner prescribed for approval of contracts, or, in the case of contracts made after the effective date of this section, by an express provision in the contract making the contracting agency subject to the provisions of this section.