(1) If a document is being amended under this part, the amendment takes effect on and from the date of the document being amended.
(2) However, an amendment including or substituting a cause of action arising after the proceeding started takes effect on and from the date of the order giving leave.
(3) Despite subrule (2) , if an amendment mentioned in subrule (2) is made, then, for a limitation period, the proceeding as amended is taken to have started when the original proceeding started, unless the court orders otherwise.