Anyone help?

I came across this photo of coach A716 ABB as United 1037.

Ive only ever known it as Northern 7016 and VFM/Go Ahead Northern 5116.  I can't ever recollect it being referred to as ex United in any Fleet lists or handbooks. 

Can anyone tell me when did this and the remainder of the batch 717-720 pass from United to Northern and the reason why?