Was there any point in GWR taking three c2c units if they can only ever use two of them on any given day on the Newbury diagrams? The third unit would appear to be only able to act as cover for the two in use. (I concede that c2c only need three, not four.)
With 2+ months of hindsight, probably not - but although the differences were known, the effect on compatibility was not. The backdrop of them (and the slower to arrive /2s) was a much more significant drop in the IET fleet availability than has ultimately manifested - we were desperate to get our hands on absolutely everything we could.
As you rightly say, c2c only need 3 sets, so at this stage even if they’re having a relatively easy time of it the 3 sets aren’t being missed by them. If that changes they may well go back, especially once the last 2 Ex- GX sets are accepted (205/206)
Perhaps perpetuated somewhat by myself, and not wording things correctly the restriction is not Newbury work only. It is
4 car work only (or boxed both ends within a 12 car) - it’s just that typically, only the Newburys run as 4 cars so that’s where they’ve appeared.
And we can, and have used all 3 at once - there are 2 fixed diagrams which are 4 car Newbury work for the /3s, and there’s now another new Newbury diagram which they could work the vast majority of solo so you could have all 3 out that way (and we did at one point last week) - we’ve not yet availed ourselves of the opportunity but as above we can run them in 12 cars.