Since the goods you are dealing with are exempted from tax under the State Act, you will not be eligible to avail input tax credit as SGST under the SGST Act, 2017 on your stock of goods lying on the appointed day. But, you will be eligible to enjoy CENVAT credit as Central Tax on your stock if you have invoices or other prescribed documents evidencing payment of excise duty under the existing law and such invoices/prescribed documents were issued not earlier than twelve months immediately preceding the appointed day.
Your product was not unconditionally exempt from the whole of the duty of excise under the Central Excise Tariff. If you do not possess invoices/other documents evidencing payment of excise duty in respect of your stock of goods, you will be allowed to avail input tax credit on goods held in stock on the appointed day at the rate of 40% of the central
tax on your intra-State supply of goods after the appointed day or 20% of the integrated tax on your inter-State supply of goods after paying central tax/integrated tax on such supply. You are allowed to enjoy the scheme for six months from the appointed day or till such stock is sold out, whichever is earlier, and tax paid by you shall be credited as central tax in your electronic credit ledger.