Yes that is correct Terry, you describe the situation exactly as it is happening now every day.
some apartment (the older one) the access card can be duplicated for a cost ~ $50 - 80.
putting it into the mailbox is also a good way to share it, so that only the mailbox key is shared or duplicated.
I also see some people access to the apartment through the garage to avoid the patrol guards.
Sounds like an acknowledgement that something's not quite right!
Yes, it happens in Regis 1 2 3 apartment in Castlereagh Sydney
the living room is partitioned and also the sunny room is covered by cardboxes / newspaper for shared by 2 persons.
Cool - it gets better!
As Aaron pointed out, tenants may not sublet without formal landlord approval.