11. The Consumer Price Index for a year is the yearly average computed on the basis of the monthly Consumer Price Indexes for Canada established by Statistics Canada for the 12 months preceding 1 November of the year preceding the year for which the Index is calculated.
If, on 1 December of a year, the data furnished by Statistics Canada are incomplete, the Commission may use the data then available to establish the Consumer Price Index.
If Statistics Canada uses a new method to compute the monthly Consumer Price Index by modifying the time basis or the content basis in question and if that modification entails a variation of more than 1% in the yearly average, the monthly indexes used to establish the yearly average for each of the years affected by the change of method shall be adjusted by the Commission in such a way as to take into account the data according to the method used by Statistics Canada on 19 August 1985.