Rectification of favorable assessments: audit-accepted departmental findings must be implemented despite expiry of the ordinary rectification period. Where an error in favour of assessees is pointed out by internal or revenue audit parties and accepted by the department as final, authorities concerned must rectify the error even if the rectification falls beyond the statutory rectification period; departmental acceptance creates a duty on assessing authorities to amend assessments in favour of assessees notwithstanding the ordinary time-bar under the assessment rectification procedure.