(a) Proof of service of process must be filed promptly and in any event
before action is to be taken by the court or the parties. The proof must show the
day and manner of service and may be by written acknowledgment of service, by
certificate of the person who served process, or by any other proof satisfactory to
the court.
(b) Failure to prove service as required by this rule does not affect the
validity of service. The court may at any time allow the proof of service to be
amended or supplied unless it clearly appears that to do so would result in material
prejudice to the substantial rights of any party.
