Input Tax Credit discrepancies: procedural certification and documentary verification required to validate ITC claimed when not reflected in supplier records. Where GSTR-3B ITC exceeds GSTR-2A due to supplier non filing, misreporting, misclassification or wrong GSTIN, the proper officer shall obtain invoice details and verify statutory eligibility criteria: possession of tax invoice, receipt of goods/services, payment to supplier including tax, absence of required reversals, and timeliness of claim. If tax payment by the supplier must be verified, differing documentary requirements apply by quantum: above a monetary threshold requires CA/CMA certificate with UDIN; below that threshold requires supplier certification. Misstated GSTINs must be notified to the supplier's jurisdictional authority, while the actual recipient's entitlement is determined independently.