Where the Indian Oil Corporation Limited or Bharat Petroleum Corporation Limited or Hindustan Petroleum Corporation Limited, makes sales of Superior Grade Kerosene Oil (PDS) to the Oil Marketing Companies in West Bengal during the period commencing from the 1st day of April, 2005 and ending on the 31 st day of August, 2010, it may, for the purpose of determination of turnover of sales on which tax is payable, deduct under clause (c) of sub-section (1) of section 16, from its turnover of sales sixty eight per centum of that part of turnover of sales which represents sales of Superior Grade Kerosene Oil (PDS) to the Oil Marketing Companies for resale in West Bengal. Provided that, no such deduction shall be allowed unless the dealer, namely, the Indian Oil Corporation Limited or Bharat Petroleum Corporation Limited or Hindustan Petroleum Corporation Limited, selling the goods, on demand by the appropriate authority under the Act, furnishes the relevant tax invoice or invoice or cash memo, or bill and other related documents evidencing such sales.