I might be overcomplicating things but it would make a hell of a lot more sense to send 9 (all 64 plates) to Darlington then do:

1584-1589: Darlington to Ashington
1537/1540-1542: Ashington to Darlington
1430: Darlington to Stockton
1512/1513: Ashington to Durham
09 Plate Pulsar's: Darlington to Redcar
1412/1413: Durham to Redcar

It would mean improvements for both Ashington and Darlington, and in turn send the oldest Pulsar's to Redcar where they can make a business case to get them out the fleet.

Would remove some ridiculous micro fleets which are around and batches split all over the place. If there's finally an resolution to the problems at Darlington then send 2 15 Plate Streetlite's more to Durham and send 1579/1580 to Ashington and finally get shot of the Solo's which are a waste of space the past few weeks, similar with 1543 eventually joining the rest at Darlington sometime aswell.