Yes the numbers do locate a specific area. I think the whole purpose of the zip codes and postal codes for Canada and other side of the pond folk is to make them sortable by machine. I notice also that if the zip does have a four number extension, in many cases that extension is the same as a PO Box number, if one is used. All I know is all the bills that are addressed to me, (and some that aren't) seem to find their way safely to my mail box.

I have not trusted the US Postal service since I was in the Army. I was young and foolish back then when I sent home a packet of irreplaceable photos. They never arrived and the fellow that took the pictures and had the negatives shipped out to Nam shortly after taking them and never returned.