Such disclaimer shall be filed at any time after the creation of the interest, but in all events within nine (9) months after the death of the person by whom the interest was created or from whom it would have been received, or, if the disclaimant is not finally ascertained as a beneficiary or his interest has not become indefeasibly fixed both in quality and quantity as of the death of such person, then such disclaimer shall be filed not later than nine (9) months after the event which would cause him so to become finally ascertained and his interest to become indefeasibly fixed both in quality and quantity.