Revision of orders deemed erroneous when assessing officer omits required inquiries or contradicts binding directions, enabling revenue revision. An Explanation is added deeming an assessing officer's order erroneous and prejudicial to revenue where the officer omitted required inquiries or verifications, granted relief without inquiry, failed to follow Board directions under section 119, or contradicted a jurisdictional High Court or Supreme Court decision adverse to the assessee; the Principal Commissioner or Commissioner may, on that basis, consider the order erroneous for revision purposes.