Production of additional evidence limited; Commission may permit documents or witnesses for reasons recorded and rebut opportunity. Regulation 43 bars parties from adducing oral or documentary evidence before the Commission that was in their possession but not produced before the Director General; however, the Commission may, for reasons recorded, allow such evidence if needed to enable orders, for substantial cause, or if the Director General denied sufficient opportunity. The Commission may direct where evidence is to be adduced, require compliance and transmission of records, and must provide admitted additional evidence to other parties with an opportunity to rebut.