(02 Sep 2015, 2:07 pm)aureolin wrote Day rover is valid on Northern rail between Blaydon and Sunderland. The Explorer is only valid between Newcastle and Sunderland.
Northern Rail customer services told me that the Day Rover is valid Newcastle to Sunderland and the Explorer Blaydon and Sunderland. The conductor on the train we used confirmed what NR said.
EDIT: Sorry, just re-read the email and it states that both tickets are valid Sunderland-Blaydon.
I think that they use Newcastle-Sunderland just for clarity.