(16 Feb 2016, 11:41 pm)S813 FVK wrote Aha. Ive worked out what it is.
There was a time when the X8 was withdrawn and replaced with an extended 8 running from Castleside to Chester-le-Street (had previously changed to an X8 at Stanley). The 8 was later extended back to Sunderland, via the same route as previously (and also the X2 route) and replaced with service V8 between Stanley and Castleside.
That will be how the X2 was replaced.
I think it was, the first set of branded buses has gone out of my memory, i can't remember much of the routes etc.