I don't think that's quite correct, and is an important point -- I believe the validity is one year from the ticket issuance date (although perhaps not controlling in your specific case to Australia given their visa time limits). Others please correct me if wrong?
Good question. I'm not exactly sure. I seem to remember them telling me from the departure date, but it's definitely worth asking the reservation agents.
Since I bought the ticket shortly before departure, this wasn't an issue.