((a)) In simultaneously contested claims where one is allowed and one rejected, the time allowed for the filing of a notice of disagreement shall be sixty days from the date notice of the adverse action is issued. In such cases the agency of original jurisdiction shall promptly notify all parties in interest at the last known address of the action taken, expressly inviting attention to the fact that notice of disagreement will not be entertained unless filed within the sixty-day period prescribed by this subsection.

((b))

((1)) The substance of the notice of disagreement shall be communicated to the other party or parties in interest and a period of thirty days shall be allowed for filing a brief or argument in response thereto.

((2)) Such notice shall be forwarded to the last known address of record of the parties concerned, and such action shall constitute sufficient evidence of notice.