On July 1, 1978, and on July first of each subsequent year, each employee and the spouse of each deceased employee who had elected the husband and wife retirement income option, retired under the State Employees Retirement Act on or before June 30, 1975, shall be entitled, in addition to his original monthly retirement salary plus cost of living allowances from date of original retirement, to an additional five per cent cost of living monthly allowance computed on the basis of his combined monthly retirement salary and cost of living allowances, if any, to which he was entitled as of the June thirtieth immediately preceding. If on any July first, the Retirement Commission determines that the National Consumer Price Index for urban wage earners and clerical workers for the previous twelve-month period has increased less than the cost of living allowance provided by this section, the cost of living allowance provided by this section shall be adjusted to reflect the change in such index provided such cost of living allowance shall not be less than three per cent.