No act or proceeding of the Appellate Tribunal shall be invalid merely by reason of—

   (a)  any vacancy in, or any defect in the constitution of, the Appellate Tribunal; or

   (b)  any defect in the appointment of a person acting as a Member of the Appellate Tribunal; or

   (c)  any irregularity in the procedure of the Appellate Tribunal not affecting the merits of the case.