(1)When an instrument brought to the Collector under Section 31 is, in his opinion, one of a description chargeable with duty, and -(a)the Collector determines that it is already fully stamped, or(b)the duty determined by the Collector under section 31, or such a sum as, with the duty already paid in respect of the instrument, is equal to the duty so determined, has been paid,the Collector shall certify by endorsement on such instrument that the full duty (stating the amount) with which it is chargeable has been paid.
