Data Point:
Our reservation, booked on Priceline, seems alive and well, accessible on both NZ and UA websites.
I have PNR and ticket numbers. Booked in the following fare classes:
BOS-LAX, W
LAX-AKL, L
AKL-SFO, S
SFO-BOS, L
Within hours of making the reservation, I went online to the NZ website and selected seats, purchasing "premium" seats for each of us ($50 each way on the long-haul legs).
This morning, I just called and added KSML for each of us. The agent was very friendly and didn't make any mention of any concerns about my reservation.