Transitional input tax credit rules govern refunds, credit carryforwards and recovery as arrears on pre-existing tax liabilities. Transitional provisions require returns of certain pre-appointed-day sales to be eligible for refund if returned within a specified period and identifiable, treat returns by registered persons as supplies, allow supplementary invoices/debit notes for upward price revisions and credit notes for downward revisions subject to recipient credit reduction, direct that pre-appointed-day claims and proceedings be disposed under existing law with refunds in cash and unrecovered amounts recovered as arrears under this Ordinance (not admissible as input tax credit), and permit agent credit for principal's goods on specified conditions.