It seems to change roughly as often as the TOC changes its socks (or station nameboards, at least). The on board announcements on Class 185s definitely say "Cark & Cartmel".
It probably makes sense to drop the suffix completely, because if going to Cartmel you're better off getting off at Grange where you might have a hope[1] of a taxi or (during the day) bus connection.
OK, if you're walking the walk from Cark is a bit nicer (done it myself), but who on earth would be walking that (a short hike, really, requiring appropriate clothing and a torch at night) who hadn't already looked at a map to decide which station to use?
[1] No guarantee - the taxis are mostly one man bands and you have to ring round, and if they're booked, they're booked - there is no big taxi firm operating any nearer than perhaps Ulverston or Barrow.