Uniform Civil Procedure Rules 1999

If a document is being amended under this part, the amendment takes effect on and from the date of the document being amended.

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.

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.