Box lobbies also have their own postcode, as do private bag locations and RD runs. In some cases an address like "Bob Bog, Invercargill 9875" might actually get it there.
If your item has a postcode, and enough other information to identify a unique address, you'll probably get the item. Post has even been known to use the phone book to track down addresses that can't be read or are incorrect.
But, that's only NZ Post. If your parcel comes via another carrier, they may do things differently.