Input tax credit reconciliation: require documentary verification and supplier certificates where ITC claimed is absent from counterparty records. Where ITC claimed in Form GSTR 3B does not appear in Form GSTR 2A owing to supplier non reporting, omission, misclassification or wrong GSTIN, the proper officer shall obtain invoice details and verify statutory ITC conditions: possession of invoice, receipt of goods/services, and payment including tax; check reversals under relevant provisions and time limits; and verify supplier tax payment by requiring CA/CMA certificate with UDIN above a specified difference threshold or supplier certificate below that threshold, subject to a proviso limiting relaxations for certain late claims in FY 2017 18.