I'm still waiting for Pevensey Bay. Only ever seen one passenger board, and have never sold or seen a ticket for there. When the one punter boarded ran up hoping to break my duck, alas he had a Eastbourne - Bexhill season.
What does "break my duck" mean?
Incidentally, when I'm in Cornwall in April, one of my excursions was planned to be the Liskeard to Looe branch line, and I had considered boarding at Coombe Junction Halt on one of the handful of trains that stop there, just for the added oddity.
I had read a report on a blog belonging to someone who wants to visit every railway station; and he mentioned that when he got on there, the guard was similarly eager to be able to issue a ticket from that station, but alas, the blogger had a ticket already.
I will probably have a Ride Cornwall that day, but after reading not just the blogger's account but your post, I think I shall purchase a ticket from Coombe Junction Halt to St Keyne Wishing Well Halt, for the guard's benefit

I doubt I'll get off at SKN, though, as the blogger did - I don't particularly fancy the walk to the next stop and the wait, since I'll probably have a bit more track to bag that day! But we'll see.