As with all things QR, it’s not quite so black and white!

It’s my understanding that buying up to business class (more than 14 days before departure) will re-ticket into a business class fare and come with the assigned fare privileges.

Special offer upgrades (less than 14 days before departure) will retain the underlying rules of the originally purchased fare and will not qualify for extra luggage / premium lounge access etc.

(…of course, it may not be until the Garden lounge turns you away that you find out which one you purchased )