To be completely fair, all of the 9/9As start and finish at Sunderland... They're Percy Main operated. It could have been changed, but it hasn't been.
Likewise, the 2A/C is the same if I'm correct... Those services have been with Deptford for quite some time now, not Washington.

I'm not trying to say that the X7 will be operated by any other depot, but we really can't judge from where services start/terminate alone - regardless of if the services are old and were previously operated by another depot or not.