I just got assigned a Postcrossing partner whose address did not include a name nor a street, just a PO box number, city, state, and ZIP.
And that made me wonder, if it would get there without a name, would it also get there without PO box number, city and state? That is, just with the ZIP+4? In this case, the PO box number had only four digits, so the +4 portion was identical to the PO box number, so you could extract it from there… and presuming that the five-digit ZIP portion was used only for PO boxes in that city, the ZIP+4 should uniquely identify that particular box.
I don’t think I’ll try it out this time, though.