Except as otherwise provided in these Supplementary Provisions, the provisions of the Income Tax Act as amended (hereinafter referred to as "the new Act") apply to income tax for tax year 1990 and subsequent tax years, and the provisions then in force continue to govern income tax for tax year 1989 (meaning the tax year covering the period from January 1, 1989 to December 31, 1989) and prior tax years.