GSTR-2B is a static ITC statement generated on the 14th of every month. Unlike 2A, it does not change once published — which is exactly why an auditor treats it as the anchor for input tax credit reconciliation.
Start with the three usual suspects: (a) suppliers who filed late and slipped into next month's 2B, (b) suppliers who filed under the wrong return type (IFF vs 1), and (c) invoices where the recipient GSTIN was keyed incorrectly. Together they account for ~70% of ITC leakage we see in mid-market clients.
Match your purchase register to 2B at invoice level, not aggregate. Use a delta report — invoices in books but not in 2B (chase supplier), and invoices in 2B but not in books (record and claim). Anything unresolved for two consecutive months should be escalated.
The 180-day rule bites quietly: if the supplier isn't paid within 180 days of invoice date, the claimed ITC must be reversed with interest. A simple aging report on the payables ledger catches this before your auditor does.