Here are UK regulationsWhatever the mass of the caravan its nose load transfers to the car, and doesn't become part of the towed load. So even at 1400kg the nose load can be deducted, but of course the OPs car is limited to 1300kg towed load.
If the overall weight of the trailer were to be treated as towed weight one would not be able to add the weight of the car to the towed weight to establish the train weight. Any regulation worded on such a basis would therefore be completely illogical. Surely the legislators in New Zealand or anywhere else aren't that naive.
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Towing with a car
Towing trailers, caravans and horseboxes with a car, including the weight and size limits, and what licence you need to have
Thought there would be bit more detailed. If car manual says 1300kg max braked then that is it.
Nothing about towing 1400kg trailer when it is applying 100kg downforce to towbar. If you can find regulation that applies to this please post link.
Here is NZ.
Guide Safe Loading Towing | NZ Transport Agency Waka Kotahi
NB manufacturer rating can be ignored. The legal requirement is stopping distance 7m at 30kmh.