(a) By the Board. Where a case is remanded, such additional proceedings shall be initiated and such other action shall be taken as is directed by the Board.

(b) By a court. Where a case has been remanded by a court, the Board may proceed in accordance with the court's mandate to issue a decision or it may in turn remand the case to an administrative law judge or deputy commissioner with instructions to take such action as is ordered by the court and any additional necessary action.