Transitional input tax credit rules govern refunds, credits and recovery treatment on migration to the new GST framework. Transitional provisions permit refund or credit treatment for tax paid under prior law where returned goods are identifiable and returned within a specified period, treat supplementary invoices and credit/debit notes for pre appointed day contracts as outward supplies subject to recipient adjustment of input tax credit, and preserve disposal of pre existing claims and proceedings under the existing law with recoverable amounts becoming arrears under this Act and not admissible as input tax credit.