Air NZ (like UA) will release more inventory between AU/NZ and North America for the Dec/Jan peak season if and when they decide they are unlikely to sell it. Over the past few years that has happened from a few weeks to a few days before the flights in question. If you need to firm up your plans now or within a short timeframe you're unlikely to find more inventory released. If you can wait until Dec and fly on a few days notice, perhaps on inconvenient dates, there may be inventory released much, much closer to flights. It's a crapshoot.