Retrospective clarificatory amendments bar reopening of completed assessments under reassessment provisions merely on that basis. Clarificatory amendments introduced by the Finance Act, 2012 in section 2(14), section 2(47), section 9 and section 195 were given retrospective effect to remove doubts about statutory meaning and to state the law from the dates of their original operation. Assessments completed under section 143(3) before 1 April 2012, where no reassessment notice had been issued before that date, are not to be reopened under sections 147/148 merely because of those amendments, though any assessment or other order validated by them remains enforceable.