TightSlot, you are right ... but.
Under IATA Baggage rules it is the
delivering airline that have the responsibility of dealing with the customer in the event of a baggage irregularity. They initiate the baggage trace and deal with any damage issues. In the event it is up to them to claim from the ticket issuing airline (who has the money) who may well claim against a third airline who might be to blame.
For years airlines applied these rules to all checked through bags. However some bean counters at some airline realised that they could save a fortune if they just refused claims when a single contract (ticket) didn't exist. So, connecting carriers started to take hits, often when it was not their fault and they began to refuse connecting baggage from the airline that started this. A lot of tit-for-tat reactions means that today many airlines will not accept baggage through check with two tickets.
BA, for example, state explicitly on their web-site that they will only accept baggage with two tickets when the connecting airline is a oneworld carrier. So a NZ/BA through check is no longer possible with two tickets.
Woody, the operative words in your post are 'a few years ago'. Don't try it today.