75. Discharge in certain cases.- Notwithstanding anything contained in the Limitation Act, 1963 (36 of 1963)- (i) on payment of the amount due on a Port Trust security on or after the date on which payment becomes due, or (ii) when a duplicate security has been issued under section 73, or (iii) when a new security or securities has or have been issued upon conversion, consolidation or sub-division under section 74, the Board shall be discharged from all liability in respect of the security or securities so paid or in place of which a duplicate or new security or securities has or have been issued- (a) in the case of payment-after the lapse of six years from the date on which payment was due; (b) in the case of a duplicate security-after the lapse of six years from the date of the publication under sub-section (3) of section 73 of the list in which the security is first mentioned or from the date of the last payment of interest on the original security, whichever date is later; (c) in the case of a new security issued upon conversion, consolidation or sub-division after the lapse of six years from the date of the issue thereof. | 
