https://www.youtube.com/watch?v=OmtSI3N57kM Auckland, like Brisbane, Sydney, Melbourne, Perth, Seattle, Edmonton, Toronto & Montreal... are just some of the cities that get to have longer train than provincial Vancouver.
https://en.wikipedia.org/wiki/City_Rail_Link
"Although the trains are capable of having extra cars added in groups of three, the CRL station platforms, as originally specified, would not be long enough to accommodate nine-car trains. The proposed new capacity is 54,000 passengers per hour with the station platforms to be made longer so they can take the longer trains..." https://en.wikipedia.org/wiki/City_Rail_Link#Capacity_forecast_forces_platform_enlargements
9 car trains are possible for Auckland, because there isn't anything like a Vancouver Mind Virus (VMV) to thwart it.
https://www.cityraillink.co.nz/meet-your-stations
https://en.wikipedia.org/wiki/Waitemat%C4%81_railway_station#Capacity Proper big city infrastructure planning and development, unlike backwards Vancouver.
https://en.wikipedia.org/wiki/Waitemat%C4%81_railway_station#Electrification
In contrast is the joke that is the two car Canada_Line. There was a deliberate decision, (apparently to save money) to not have a future station level clearance of at lest 100 m, if not even 160 m. So instead of planning for at least 5 car trains, there is only enough space for a 2.5 car joke of a train, some day.
https://en.wikipedia.org/wiki/Canada_Line#Stations "The five busiest stations have platforms 50 metres (160 ft) long, while the rest of the stations have 40-metre (130 ft) platforms that can be easily extended to 50 metres."
Being that this is a line which could eventually link YVR to the Tsawwassen Ferry Terminal & eventually Waterfront station with Park Royal and even the Horseshoe Bay Ferry Terminal, the BC Mind Virus (BCMV) got in the way.
https://en.wikipedia.org/wiki/Canada_Line#Technology "The capacity of the trains is estimated at 334 people per pair of cars (comfortably) or 400 people at crush load."
Since each car is 20 m and the stations are designed to a maximum of 50 m, every effort should be made to try to eventually have 60 m platforms. Unfortunately, it might be difficult enough just to try to gradually have 55 m stations. Still, the initial goal should be to try to have a 3 car train of 60 m.
Then with Selective+Door+Operation