Do you have proof of lodgement with Aus Post? IF so, then you are OK, if you can proove items were posted, that is all you need to cover yourself against PP claims. If you haven't got proof od lodgement then you are possibly "up the creek". With Aus Post offering tracking on all parcels and now ebay labels, you still neeed proof of lodgement not just tracking number.

For regular parcels, AP have a lodgement form where the basic item info can be filled out and then they stamp it. This is acceptable proof of lodgement. For ebay satchels and labels, they should provide a printout of scanned items...never leave without it as this is your proof of lodgement...if items wont scan, ask then to enter them on the lodgement form indicating the tracking number, this becomes your proof of lodgement.

From what you say they made a note one the back of the lodgement slip for the items that did scan. What does it say and is it stamped?