(a) Application may be made by any party in interest for rehearing or reopening of a claim. Such application must indicate that:

(b) Such application must be made within a reasonable time after the applicant has had knowledge of the facts constituting the grounds upon which such application is made. The board may in its discretion deny such application without a hearing thereon or may require the applicant to submit further proof before finally passing upon said application. Allegations as to newly discovered evidence as basis for such application must be substantiated by supporting affidavits. The data to be submitted in connection with an allegation that there has been “a change in condition”, as required by paragraph (a)(2) of this section, must, except as hereinafter provided, be in the form of a verified medical report prepared as a result of an examination held after the expiration of a substantial period subsequent to the closing of the case. This report must clearly state the objective findings. If such an examination cannot be had, a rehearing may be granted upon the presentation of information in affidavit form, which would indicate that a material change in the degree of disability has taken place subsequent to the closing of the case.

(c) If the board in its discretion grants the application and orders reopening and rehearing, the case may be referred to an appropriate calendar for the taking of evidence and for such further consideration as appears warranted. When a case or any issue therein is so referred to a referee, he shall thereupon receive such evidence as is specified in the order of the board and he may then consider the case in the light of the evidence previously introduced, together with that presented at the rehearing, and may then render a decision upon the completed record, unless the order of submission limited the referee to the taking of evidence and the returning of the transcribed completed record to the board for review and decision.