20.9.2.0.2. Where a person has purchased movable property before 1 January 1991 in respect of which the tax of 9% provided for in this chapter does not apply and where he returns the property after 31 December 1990 and before 1 February 1991 in exchange for other movable property which, but for this section, would be taxable at the rate of 8% after 31 December 1990 in accordance with this chapter, the tax provided for in this chapter does not apply in respect of the purchase of the other property if the exchange is invoiced or paid before 1 May 1991.