AFAIK
1. CC of existing services can't be modified at short notice. It might require planning, trials, changes in system etc.
2. Not all VB rakes churned out might be available for service. Some might need modifications and readying the rake might take some time. Also if newer rakes are moved as per allotments, I suppose path/slot/crew arrangement is not possible at such short notice. So the rakes might be getting transferred via via.. Need tk check if they had combined a couple of 8C VB rakes together and transported it...
more... to nearest hub or otherwise