Time limits for reassessment notices: threshold-triggered extended limitation and procedural exclusions govern validity of notices. No notice under section 148 may be issued after three years from the end of the relevant assessment year, except that where the Assessing Officer has books, documents or other evidence showing escaped income represented as an asset, expenditure, transaction-related entry or book entry likely meeting the prescribed threshold, an extended period up to ten years is available; similarly, notices under section 148A are subject to a three-year limit with a comparable extended window when information suggests escaped income meets that threshold. Time allowed to the assessee and court-ordered stays are excluded in computing limitation, and specific deeming and transitional rules apply.