I wonder why all the Pendo didn't get extended to 10-car, with a few (but less) as 11-car? I'd rather see a few fewer 11-car, but no more 9-car. It's not so bad now 1 more carriage has been converted from First to Standard, but it's still a bit unbearable when a service has been cancelled.
10-car Pendolinos didn't work, because of the equipment needed under each coach or pair of coaches.
The 9-11 car upgrade was the grudging DfT approval of 106 new Pendolino vehicles (31x2 plus 4x11), in, I think 2010.
This was a last gasp order with Alstom, as production of more vehicles of that type would not be possible.
DfT placed the order, and then got Virgin to manage the roll-out.
All part of the "anyone but Virgin" attitude of the day.