The home improvement trades cited would not have offices that customers could come to, but could use their home address because, as a practical matter, that is the base from which they operate and in working with these folks I have dropped off checks or contracts for them with their spouses or older children. I am uncertain, but if post office boxes plotted at all, it would most likely be to the zip code centroid or maybe to the post office location. Do note, that landmark addresses, ones associated with building names instead of the streets on which they front and from which they are accessed, create similar difficulties, and new streets not getting on to maps until years after they are built is also problematical.