Yes I see. But National Rail Enquiries say that one change is necessary to get to Fishguard on this 8.47 service, so you either get off the leading units at Whitland and get on the rear, or, stay on the rear one from the start? Unless of course the rear unit is locked out of use until Whitland?
You'll be in the same boat as the Cambrian where the Pwhelli/Aberystwyth portions of trains from Birmingham reverse order at Shrewsbury. There are always passengers in the wrong portion on departure form Shrewsbury is its a case of get a seat where you can in the West Midlands due to high loadings and again at Shrewsbury. ATW do not label which unit goes where.
At Shrewsbury the automated announcement tells passengers for all stations to Aberystwyth to sit in the "front carriage" and for all stations to Dovey Junction and the coast line the "rear carriage" - the trains are formed of a pair of 158 units- who sits in the middle two coaches!
The more intelligent conductors do a full ticket check on departure from Shrewsbury and inform passengers in the wrong portion individually, the better ones tell them not to move until after the train has departed Newtown when passengers have got off at Welshpool and Newtown and theirs more space. The stupid ones announce which portion is which over the tannoy at Shrewsbury resulting in panicking passengers unfamiliar with the line barging luggage and rucksacks across the train and running into each other a full 80 minutes before the train splits.
The platform staff at Mach are good at herding passengers into the right portion as well and the station supervisor Elwyn will often be seen walking through the train telling people as well as the conductors. Crews change at mach and its usually the first thing the now 2 new conductors do is make sure folk are in right portion. Despite all this I've still seen people balls it up and leave for Barmouth on the Aber portion. Thankfully theirs Dovey Jnc - its not unknown for the Aber portion to wait there for the coast one to catch up and passengers finally get in the right portion there.
I wonder how ATW will manage this in West Wales?