Maybe all the 3 car-175's are in the wrong places due to the derailment in Shrewsbury over the weekend.
Yes. The diagrams are separate with the 3 Cars diagrammed to the busiest services as far as possible. Why I say as far as possible, this is difficult because the Diagram might be on a quieter service in the morning and a busier one later in the day or vice versa.Do they have set diagrams for 2 and 3 Cars?
Monday aside, it's rare to find anything other than the booked class and type on this route. If there's a shortage of 3-car units in Chester one night, then the diagrams out of Chester to South Wales the next morning usually get lumbered with 2-car sets. North Wales-Manchester gets priority for 175/1s.