The parties to the appeal shall not be entitled to produce additional evidence either oral or documentary before the Appellate Board, but if the Appellate Board requires any document to be produced or any witness to be examined or any affidavit to be filed to enable it to pass orders or for any other substantial cause, or , if the commercial tax authorities have decided the case without giving sufficient opportunity to the appellant to adduce evidence either on points specified by them or not specified by them, the Appellate Board, for reasons to be recorded, may allow such document to be produced or witness to be examined or affidavit to be filed or may allow such evidence to be adduced.