The parties may, by stipulation, agree upon any facts involved in the proceeding and include them in the record with the consent of the presiding officer. It is desirable that facts be thus agreed upon whenever practicable. Written stipulations shall be subscribed and shall be served upon all parties of record unless presented at the hearing or prehearing conference. A stipulation may be proposed even if not subscribed by all parties without prejudice to any nonsubscribing party's right to cross-examine and offer rebuttal evidence. [Rule 162.]