(25 Dec 2014, 4:37 pm)tyresmoke wrote 4644 is a generic one, with both on the rear. Saw it the other day.
4646 is indeed Darlington based, think X26/X27 branding but not 100%.
I haven't had a close look at them apart from the first day in service, I will try and find out when I'm next in Darlington. Think I may have one or two more photos that aren't on Flickr.
Different as there is often at least one missing everyday.