A decision of the Tax Court (except a decision dismissing a proceeding for lack of jurisdiction) shall be held to be rendered upon the date that an order specifying the amount of the deficiency is entered in the records of the Tax Court or, in the case of a declaratory judgment proceeding under part IV of this subchapter or under section
7428 or in the case of an action brought under section
6226,
6228
(a),
6247, or
6252, the date of the court’s order entering the decision. If the Tax Court dismisses a proceeding for reasons other than lack of jurisdiction and is unable from the record to determine the amount of the deficiency determined by the Secretary, or if the Tax Court dismisses a proceeding for lack of jurisdiction, an order to that effect shall be entered in the records of the Tax Court, and the decision of the Tax Court shall be held to be rendered upon the date of such entry.