(a) For purposes of this part, unless expressly otherwise provided, for taxable years beginning before January 1, 1984, references to the California Consumer Price Index shall mean the California Consumer Price Index for All Urban Consumers (old series).
(b) For taxable years beginning on or after January 1, 1984, references to the California Consumer Price Index shall mean the California Consumer Price Index for All Urban Consumers as modified for rental equivalence homeownership (new series).