Shows how much I travel on it! I think the last time was February/March and it was a 158. Before that it was August 2008 and a 150.
I think it was around February when I was surprised to find myself on a 175 at midnight - but 158s probably substitute sometimes.
According to the timetable the 1930 Manchester to South Wales service terminates at Cardiff Central. Do they use the same unit for the Carmarthen service then? They might as well timetable it as a through service.
I was referring to the 22xx off Cardiff by that point (not a stopper), it being another service that seems to have switched to 175. It used to run as a separate train from Cardiff, and was a pair of 150s last time I found msyelf on it - presumably to provide sets for Pembroke Dock and Swanline. Since then it's reverted to being a through service (18.30 Manchester), probably because they no longer seem to need to stable any 150s at Carmarthen.
I'd guess the 2315 is intentonally not a through working from anywhere, because it's probably a useful service for moving whatever fresh stock is needed to Carmarthen for the start of the next day.