Recovery of customs duty expanded to unpaid and short-paid cases, with an extended limitation period for non-collusive investigations. Amendments to section 28 broaden recovery to include duties that were levied but not paid or short-paid by substituting terms throughout the provision and marginal heading to reflect 'not paid' and 'short-paid,' and insert 'or paid' where needed. The changes also extend limitation periods applicable to initiating investigations and recovery proceedings for cases not involving collusion, wilful misstatement or suppression of facts, lengthening the temporal window for pursuing such non-collusive matters.