(a) Beginning January 1, 1990, each survivor’s benefit and each reversionary annuity payable under Section 16-136 shall be increased by 3% of the currently payable amount thereof (1) on each January 1 occurring on or after the commencement of the annuity if the deceased teacher died while receiving a retirement or disability retirement annuity, or (2) in other cases, on each January 1 occurring on or after the first anniversary of the granting of the benefit, without regard to whether the deceased teacher was in service on or after the effective date of this amendatory Act of 1991, but such increases shall not accrue for any period prior to January 1, 1990.
     (b) On January 1, 1981, any beneficiary who was receiving a survivor’s monthly benefit on or before January 1, 1971, shall have the benefit then being paid increased by 1% for each full year elapsed from the date the survivor’s benefit began. On January 1, 1982, any beneficiary who began receiving a survivor’s monthly benefit after January 1, 1971, but before January 1, 1981 shall have the benefit then being paid increased by 1% for each year elapsed from the date the survivor’s benefit began.
     On January 1, 1987, any beneficiary whose monthly survivor’s benefit began on or before January 1, 1977, shall have the monthly survivor’s benefit increased by $1 for each full year which has elapsed since the date the survivor’s benefit began.