Had been running for quite some time, and prior to that had been running Monday - Thursday for at least a year or two.
The issue for users now is that they have yet to establish regular 6 car workings as standard and to be relied upon.
I know of a surgeon living in Sheffield and working in Manchester. A regular first class commuter, he could accept not getting a seat and space to work once. Before Christmas he had to squat on the floor to use his laptop. Never again and he's still telling anyone who mentions railways the same story. He has a nice comfortable Mercedes and most days uses that. It runs to the timetable he sets, doesn't get cancelled and he always has a seat.
It's the same problem with any business that forgets why customers use the service or commodity, preoccupied with its own internal issues. Having worked for 3 national companies over many decades I've seen it from different perspectives. Some loyal customers will be lost if there's a viable alternative.
Sadly regular travellers are indeed being lost. Thanks to the 3 car Friday provision more are working from home on Fridays, or using the car. The result is that at my station Friday loadings are only a little over half the other 4 days. That's a much greater loss of users than for other trains on Friday compared with the rest of the week, and evidenced by the spaces in the car park at 7.30. Chicken and egg?
Provide the space and users will come back, but only when word gets round that it can be relied on.
Getting the trains to run every day and to time is probably harder than getting the extra coaches into service, but users between Sheffield and Manchester are expressing preference for EMR's 4 car 158s.