At some point today, the GNER fares for the 'to Glasgow' leg did so. It didn't take long at all for the cheapest ones to sell out (if you want to travel on the Wednesday, you can still get some £13.50 tickets...)
With a script, you could be (reasonably) sure of getting the cheapest ones the minute they become available.
I also wonder if anyone's making money out of buying up the cheapest tickets and then selling them, nearer the date of travel, for more. Unlike airlines, train tickets aren't tied to an individual's name and there are some journeys you just know will be popular enough for you not to be left with a pile of unused, 'no refund', tickets.
I'm not particularly disappointed - I was thinking of going first class anyway, and the cheapest of those tickets were still available - but I'm a little annoyed that I still haven't had the promised email from GNER saying 'you can buy them now...'