211-3 Wyo. Code R. § 3-8
Not later than twenty (20) days before the date set for oral argument, or twenty (20) days before the date set for filing the brief or written statement of a petitioner, an application may be made to the Board for leave to present additional evidence. If it is shown to the satisfaction of the Board the additional evidence is relevant to a material issue before the Board, and is not repetitious of evidence or testimony taken before the county board of equalization, and there was good reason for failure to present it in the proceedings before the county board of equalization, the Board shall order the additional evidence be taken before the county board upon conditions determined by the Board. The county board of equalization may adhere to or modify its findings and decision after receiving such additional evidence, and shall supplement the record to reflect the proceedings had and the decision made. Supplemental evidence may be taken by the Board in cases involving fraud or involving misconduct of some person engaged in the administration of the law affecting the decision.
211-3 Wyo. Code R. § 3-8