PlusBus is (or was) specifically advertised as something you could add-on for the origin and/or destination shown on your rail ticket, but not at an intermediate station.We are told so many times on this forum that a season ticket is valid for journeys to and from any intermediate station on a valid route, is it not? Yet having a perfectly valid ticket to a station does not necessarily allow the sale of a PlusBus ticket for that destination? That does not seem fair or particularly logical to me.
Doesn't mean you won't find someone willing to sell it for an intermediate point, of course, but there's no entitlement to it.