I get the impression lately that AP are trying to discourage philatelic sales through post offices as the range even at the GPO Philatelic counter is limited to only the past 3 months. And to access the philatelic counter one must join the general queue as the philatelic counter is not staffed. I find it easier to order what I need either through the Philatelic Bureau or wherever possible through my local PO who are very friendly and helpful.
This may be a local/state decision? In Sydney there is a dedicated line, though the philatelic counter serve the general line when there are no philatelic customers. The senior staff member who I deal with is more than happy to accommodate requests and always gets requirements in.
Currently the Sydney Philatrlic Centre (which is really just a service desk in the QVB PO) is closed for shop renovations - staff have been relocated with the stock to Sydney GPO in the meantime.
I do note that there have been continual supply problems with LPO's being able to access some philatelic stock and this appears to boil down to the fact that stock is allocated for regions and then relies on how a manager/distribution centre decides to allocate stock to the LPOs within that particular region.
On the topic of Annual collection, my local LPO noted to me that they have already sold more of this years collection than last years, despite the later on sale date!