D.C. Mun. Regs. r. 27-207
The Board may, in its discretion, and within the proper scope of the appeal, permit either party to amend its pleading upon conditions fair to both parties.
When issues within the proper scope of the appeal have not been raised by the pleadings but are tried by express or implied consent of the parties or by permission of the Board, they shall be treated in all respects as if they had been raised in the pleadings. In these instances, motions to amend the pleadings to conform to the proof may be made but are not required. If evidence is objected to at a hearing on the ground that it is not within the issues raised by the pleadings, it may be admitted within the proper scope of the appeal, provided, however, that the objecting party may be granted a continuance if necessary to enable it to meet the evidence.
D.C. Mun. Regs. r. 27-207