Why might someone go on appearing in a Postal Directory after they have moved from a property, or even after they have died?

Information within postal directories was either paid for by subscribers or collected by employees of the publisher who produced the directory. It is possible that someone may have paid for several years’ entries in a directory and died before the publication date. Alternatively, information about the inhabitants of a building may not have been updated promptly by the publisher.

Why might a property not be listed in a Post Office Directory?

In many cases because the owner or resident of the property did not subscribe to the directory. Another possibility is that the property is known by two addresses (e.g. occupies a corner site with an entrance at each street, and the directory only includes one of the addresses).

Why might there be only one or two persons listed at a tenement property (which should have had 6 or more households)?

Usually because the tenement had commercial properties (e.g. shops, store-rooms or workshops) on the ground floor, and it is the proprietors of these businesses who paid to be included in the directory.