(a) When any person has in~ advertently useu for an instrument chargeable with duty, a stamp of a descnption other than that prescnbed for such instrument by the rules made under this Act, or a stamp of greater value than was necessary or has inadvertently used any stamp for an instrument not chargeable with any duty; or
(b) When any stamp used for an instrument has been in advertently rendered useless under section 15, owing to such instrument having been wntten in contravention of the pro~ visions of section 13;
The Collector may, on application made within six months after the date of the instrument, or if it is not datc>d, within six months after the execution thereof by the person by whom it was first or alone executed, and upon the instrument, if char geable with duty, being restamped with the proper du1y, canw eel and allow as spoiled the stamp so misused or rendered useless.
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