Section 21. Vacancies, etc., not to invalidate proceedings of the Boards.

No act or proceedings of a Board shall be invalid merely by reason of—

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

(b) any defect in the appointment of a person acting as a member of the Board; or

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