Decoding codesharing

[John Thoroughgood]

As an infrequent visitor to YSSY, I am still trying to get a handle on a number of operational idiosyncrosies.
My biggest source of confusion revolves around the International arrivals/departures lists on the Sydney Airport site.
Example being the 0940 departure to Auckland, which shows in order from top of page, Air Canada, Air China, ANZ, Asiana, Singapore, Thai and United, all using JO1 check-in.
How does one determine which company aircraft actually operate this service? Is it top, bottom or random?
Forgive my ignorance, I know I'm a greenhorn, but I'll never learn if I don't ask.
Cheers John