Input tax credit carryforward permitted into electronic ledger subject to admissibility, deadline, substantiation-linked exclusions and refunds. Transitional rules allow a registered taxable person, not on the composition scheme, to transfer cenvat/VAT/entry tax credits shown in pre appointed day returns into the GST electronic credit ledger in the prescribed manner within the statutory deadline, provided such amounts are admissible as input tax credit under the Act; credits linked to Central Sales Tax claims that are not substantiated under the earlier rules are ineligible for ledger credit and an equivalent amount may be refunded under the earlier law when substantiation is later provided, with prescribed calculation methods for such excluded credit.