(1) Where a taxpayer elects to report income arising from the sale or other disposition of property as provided under this rule and the entire income therefrom has not been reported prior to the year that the taxpayer ceases to be subject to tax under 15-31-301 , MCA, the unreported income shall be included in the measure of the tax for the last year in which the taxpayer is subject to tax under 15-31-301 , MCA.