Input tax credit reconciliation: certification permitted to validate ITC differences when supplier records do not reflect supplies. Discrepancies between ITC claimed in FORM GSTR-3B and amounts in FORM GSTR-2A for FY 2017 18 and 2018 19 must be resolved by obtaining invoice details and verifying Section 16 conditions (invoice possession, receipt of supplies, payment to supplier), assessing need for reversals and timeliness, and requiring documentary certification: a CA/CMA certificate with UDIN where the per supplier yearly difference exceeds the prescribed threshold, or a supplier's declaration where it does not. The guidance applies to ongoing or pending proceedings and to bonafide reporting errors.