(1) The parties to the appeal shall not be entitled to produce additional evidence, whether oral or documentary, in the Commission. But if -
(a) the competent authority from whose order the appeal is preferred has refused to admit evidence which ought to have been admitted, or
(b) the party seeking to produce additional evidence, establishes that notwithstanding the exercise of due diligence, such evidence was not within his knowledge or could not, after the exercise of due diligence, be produced by him at the time when the order appealed against was passed, or
(c) the Commission requires any document to be produced or any witness to be examined to enable it to pronounce order, or for any other substantial cause, the Commission may allow such evidence or document to be produced, or witness to be examined.
(2) Wherever additional evidence is allowed to be produced by the Commission, the Commission shall record the reason for its admission.