It's a strange one Rock. It's been listed as "allocation exhausted" for months and yet a couple of days before the game there are suddenly tickets available...
Yep, as Jeb said it's the corporate tickets that have to be allocated at the start of sales period and there are always some the corporates don't decide to use - so they have to give them back and they go on sale a day or two before the game. They have to put allocation exhausted because they have to assume all the tickets are unavailable until they know for sure.
Pretty sure the Sydney matches would have the same deal - but as they never actually sell out all the available tickets, it's not as obvious [icon_razz1