Thanks all. I booked my US connecting flight on United to use the Star Alliance interline benefits. Unfortunately United cancelled my flight and put me on a later flight that risked me and/or my bags missing the connection to my Air NZ flight. To avoid this I’ve swapped to an earlier option, but it is operated by a United partner airline called JSX, which does not appear to be a partner for Air NZ or to interline with others (as it is based away from the main LAX terminal complex). I’ll ask on the day and report back.