(19 Apr 2021, 7:38 pm)mb134 7518 made the transfer to Darlington late last year if I remember correctly, think it was either due to an extra decker being needed for capacity on a certain board or due to a board transfer between the two depots.
Not sure on 2856, looking at Bustimes data I'd assume it transferred from Jesmond in anticipation of the April service changes.
7518 like you say was for extra capacity on the 1/5/5a school time boards - released from Durham after they swapped the 58 reg E400's for the B7 Gemini's
2856 was released from Jesmond after Arriva lost the contract for service 6 in Newcastle - replaced 2822 at Darlington which was on loan from Jesmond due to vehicle shortage.
