Its potentially possible for individuals/orgs too. The post office standard mentions something to the effect "If a firm name is assigned a unique ZIP+4 then it

Its potentially possible for individuals/orgs too. The post office standard mentions something to the effect "If a firm name is assigned a unique ZIP+4 then it must be used" (rather than just the zip code). Which implies its possible for a "firm" to get their own zip+4 number and that by itself is probably sufficient for the automated mailing system to identify the recipient. The ZIP+4 is intended to be a redundant checksum against the name+address (which doesn't strictly require a zip code for handwritten/non bulk mail), so presumably a bunch of "hacks" work in the post office system as well. AKA, for a lot of rural/etc places just a name and a basic zip code probably works/etc.