"No card in letterbox"
Yes - VERY possible!!
My seller friend likes to check up and see where their registered items are for buyers who haven't informed them of receipt. Just last week, there was one customer who had TWO registered parcels waiting for them at the post office - but they had NOT been left a card for either. One of them had been there for nearly two weeks and was in danger of being "returned to sender".
Fortunately, my seller friend contacted the buyer to sort out the situation - which I have no doubt saved them from an undeserved reaction from the buyer. Needless to say, the buyer was none too pleased with Australia Post about the matter, but did get their items and were thankful of my seller friend's efforts.
Another local story is an example of delivery short-cuts that just gets you angry.... There is a guy who get a number of items sent to his 90 year-old father (who lives in our area), because he cannot ensure his whereabouts to take delivery, but his father is ALWAYS home and is happy to oblige.
However, the contractor who was meant to deliver a particular parcel apparently has this rather poor habit of driving up to an address and if it LOOKS like nobody is home, simply leaves a card. No knocking on a door. Needless to say, the 90 year-old had to traipse up to the post office to collect the item (which I believe was bulky and awkward) when all he should have had to do is accept it at his front door. Apparently, even the post office staff know this gentleman and were appalled at seeing him having to go through all this - because of some lazy, selfish contractor.