Any pension that has been determined to have been incorrectly calculated after an individual begins receiving such pension shall be adjusted as follows:
(1) If an individual’s pension is determined to be less than he or she is entitled to receive, it will be adjusted retroactively to the effective date of the pension.
(2) If an individual’s pension is determined to be more than he or she is entitled to receive, it will be adjusted prospectively only.
(3) In no case shall a pension awarded under this chapter which has been in effect for 1 year be subject to reduction.