Whenever in respect of any proceeding under this Act any gift-tax authority ceases to exercise jurisdiction and is succeeded by another who has and exercises such jurisdiction, the authority so succeeding may continue the proceeding from the stage at which the proceeding was left by his predecessor:
¹ Provided that the assessee concerned may demand that before the proceeding is so continued the previous proceeding or any part thereof be reopened or that before any order of assessment is passed against him, he be reheard.