Originally Posted by
Platy
Are you able to share whether this "rule" is a written one and publicly advised on the QF web site?
It is specified in the lounge access criteria for the Auckland Qantas International First lounge page (and in similar specific pages for other lounges as well).
Lounge Locations | New Zealand | Auckland International Airport | International First | Qantas.com
Lounge Access and Eligibility
Eligible Class of Travel
...
Eligible Qantas Members
Platinum Frequent Flyer
Next onward flight must be on a Qantas^, Emirates^, Jetstar Airlines+ or oneworld operated and marketed flight. #
One guest allowed and must be travelling with the member on the same flight.
...
Eligible oneworld Status
^ Lounge access eligibility is based on the class of travel, Qantas club membership or
the Frequent Flyer Membership tier for your next onward flight.
The last part of the ^ footnote refers to the membership frequent Flyer Program the PAX is crediting to.
i.e. To be using Qantas FF Platinum status to enter this Lounge before a QF/EK flight the QF Platinum member is supposed be crediting the travel to QF.
n.b. There is no such caveat when traveling oneworld (other than QF) so the OP as a QF WP can Access the First Lounge before a LA flight while crediting to QR.