I'm pretty sure UA has a zed agreement with NZ, we at US have a high zed agreement. It is the most expensive zed agreement, not sure what agreement UA and NZ have. Not sure if you are familiar with the ZED process, but it works like this - you purchase your zed ticket (not sure if NZ is using paper or electronic) from your employer. Then you list for the flight and cross your fingers the flight looks good, then you either make it or you don't. As easy as that.