Waitlisting on any flight prior to 25 May means that you are categorised in status first (CL, Plat, Gold, Silver, Bronze) then within that status, the order in which you applied for the waitlist. Therefore, first in, best opportunity AND waitlists can clear prior to the flight date.
Post 25 May everybody waitlists and the waitlists are decided on the flight day (or after midnight the night before?) by Yield Management and processed at check-in. They are decided purely on status (but presumably also in order they were requested, this isn't clear yet).
So you best hope is to waitlist and hope it comes through by 25 May; otherwise it is not clear whether on 25 May the system will change for waitlists to include the new system for all flights post 25 May (thus losing the protection of pre 25 May rules).
Qantas has told me that if you waitlist pre 25/5 you will have priority over the 2nd waitlist which will be decided on priority. It sounds like Lindsay has been told something else so who knows..........
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