No VAT on basis of provisional invoices of LPG when its price subsequently fixed by Petroleum Planni

CST & VAT : Where assessee-company was engaged in manufacture of LPG and it at time of supply of LPG to oil companies issued provisional invoices and after receiving information from Petroleum Planning and Analysis Cell [PPAC] about final price of LPG fixed by it issued final invoices by issuing credit or debit notes, sale price of LPG in case of assessee would be price fixed by it after deduction in primary invoice on basis of credit notes issued subsequently