If any instrument chargeable with duty and not duly stamped under this Act, is produced by any person of his own motion before the Collector within one year from the date of its execution or first execution, and such person brings to the notice of the Collector the amount of the proper duty, and offers to pay to the Collector the amount of proper duty or the amount required to make up the same, and the Collector is satisfied that the omission to duly stamp such instrument has been occasioned by accident, mistake or urgent necessity he may, instead of proceeding under section 37 and 44 receive such amount and proceed further as hereinafter provided:
Provided that where any instrument executed or first executed is brought to the Collector after the expiration of one month from the date of its execution or first execution, such instrument shall be chargeable with duty as applicable at the time of its presentation before the Collector under this section.