I never understand the Amex Plat / Centurion 2 for 1 situation.

Neither passenger is booked in I class (the Business redemption category). Both are booked into Z class (I think), so how do they know who has or hasn't paid?

From Australia, the Amex deal doesn't work out financially anyway for the Pacific islands, PPT or HNL but it is the cheapest way for 2 pax to get to LAX or SFO.

AA does give both passengers miles, but AC and UA don't. What does NZ do?