¹[83A. (1) An officer of Customs not below the rank of an Assistant Commissioner of Customs may from time to time make or cause to be made such amendments to an assessment of duty or to the value taken for the purpose of assessment of duty as he thinks necessary in order to ensure the correctness of the assessment even though the goods to which the value or the duty relates have already passed out of Customs control or the duty originally assessed has been paid. (2) If the amendment has the effect of imposing a fresh liability or enhancing an existing liability, a demand notice in writing shall be given by the officer of Customs to the person liable for the duty. (3) Unless otherwise specified in this Act, the due date for payment against the aforesaid demand notice shall be thirty working days from the date of issue of such a written demand notice by the officer of Customs.