I get your logic, but 57 trains are only useful if they are in correct place, adding extra carriages to trains where they are not scheduled and not required doesn't make it ok. That's insulting to schedulers to say you got it wrong so adding to train length, simply because operators can't deliver what is scheduled.
It's not a total quantity thing, it's about having sufficient of the right type of unit in the right place. Misbalance is polite way of saying got insufficient where needed. Pretending that because there are some elsewhere then job is satisfactory, it's very low quality standard. You wouldn't say wasn't a rail adhesion train, buts it's ok sent two along another line, so why do you think its acceptable that a different standard should apply.
Your application to be a stock controller on GWR is awaited.
It’s not a case of “adding extra carriages” but having to deal with what you have on the day when you get numerous NR and external issues that alter your plan (as well as the usual unit and crew related problems) and very little chance to rectify the situation to send the right units out the following morning. Imbalances are quite common with the amount of outstation locations that GWR have for Bristol workings and the variety of formations and types that GWR have.
The prime objective is not to cancel trains so you will do things like put a layover 3 car onto the next leg of a delayed 2 car working and vice versa when the 2 car eventually appears. What goes to bed at the outstations comes back out in the morning - there is no other option and, in the case of Bristol SPM, a very large proportion of their units start the day at the outstations and there are not many options to swap units back at Bristol either.
This morning there were imbalances at Fratton, Westbury, Weymouth, Gloucester and Exeter. Your problem with 1F11 was because of the imbalance at Westbury which ended up on Sunday night with a 2 car instead of a 3 car. Outstations don’t have spare sets and it would be unreasonable to expect them to have that kind of provision.
If GWR had fixed formation 5 car units on Pompey-Cardiff and Cardiff-Penzance and 3 car and 4 car units for the rest of their services, all of one type, it would be much easier to operate, even if you get a raft of issues mucking up your days operation.