Transitional input tax credit rules govern refunds, recoveries and credit admissibility after the GST appointed day. Transitional rules govern refunds and input tax credit where transactions or proceedings span the appointed day: returned goods within prescribed periods may be refunded under the existing law; price revisions under pre-appointed-day contracts allow issuance of supplementary invoices, debit notes or credit notes with corresponding tax adjustments; refund claims and existing-law proceedings are to be disposed of under the existing law with refundable amounts paid in cash and recoverable amounts treated as arrears under this Act and not admissible as input tax credit.