I've noticed that some services have a station call that is timetabled as "Service stops to pick up passengers only" (or "drop off passengers only"), e.g. the 23:30 Caledonian Lowland Sleeper at Watford. Is this just for timetabling to try and make sure the train isn't full of people trying to do that leg? If someone gets on at EUS with a EUS-WFJ ticket would they technically have an invalid ticket?