In Victoria an owner, resident or not, can give a PO box number (or any address at all) as their mailing address.
So in reality an OC can sometimes not be sure if a lot is owner occupied or let out. This situation actually exists for one of the apartments in the building where I am on the Committee. But the owner must, by law, must always be contactable (by a mailing address at least).
So my point was, can’t you serve the owner when an ‘occupant’ is to be served a notice? In Victoria at least, it seems that sometimes you have no choice but to do exactly that if you have no idea who the ‘occupant’ actually is.
Maybe you can do this in other states too?