(1) The selling dealer shall issue to the purchaser a supplementary tax/sale invoice in respect of any escalation in the price of the goods sold previously as soon as the amount of such escalation, whether interim or final, is settled between the two. The invoice shall contain reference of the original invoice(s) issued previously in respect of the sale of the goods.
(2) A supplementary tax/sale invoice issued under the circumstances when the agreement of sale provides for escalation in the price of the goods sold and the final prices of the goods could not have been determined at the time of their original sale, shall, for the purposes of the Act and these rules, be treated as a fresh invoice and shall be given effect accordingly, otherwise, the invoiced amount shall be added back to the gross turnover for the tax period in which the original sale was made and shall, notwithstanding any limitation, be assessed to tax.