It wasn't intended as that! It was intended as a question, which is why there are question marks! I tried to make sense of what had happened on the Northern train, as I thought that, originally, the customer was on a single ticket, or outward portion of a return, and was refused an excess. I think I may have misread an earlier thread from August 2009, which says that a ticket cannot be excessed once you have reached the destination.
http://www.railforums.org.uk/showthread.php?p=341425
Of course, it was a single ticket being discussed there! So, just to make it clear in my own mind, it's correct that over distance excesses can be bought on the return from a station that is further away, but on the same route as the original destination? So I could, therefore, buy a ticket to Edinburgh and excess my ticket to return from Inverness?