OK that's really good to know. I often fly a combination of United/Skywest and upgrade just the United portion so I assumed I could do so with this trip as well since it's all booked through United. I'll remember this in the future. And, you all are correct - the SFO to CHC is United, not Air NZ. I think NZ is a LAX to AUK leg which we've decided not to do.

Thank you for the help.