We got a post code issued _ same as our neighbours each side and opposite and we were registered.
I think that technically a post code covers all the properties on a "walk" (or some such Post Office term) and ties in to how mail is sorted at the last stage in the local delivery office & put into the postie's mail bag? In less rural areas there was often one code for one side of a street and another code for the other side. At least I understand that's how it used to be. Maybe things have changed...