I've had a look at the page that crehld linked to for a journey I'm planning to do in the summer, so as to avoid starting a new thread on something similar.
I have a student railcard, which will be used for travel between Barnhill/Glasgow Central - York or Doncaster. I am thinking of the possibility of either BNL/GLC - DON 1st Advance (33% discount), or BNL/GLC - Alnmouth for Alnwick 1st Advance plus the Freedom of the North East Rover for the remaining leg to YRK or DON.
Regarding the upgrade from Standard to 1st with the rover, would it be the difference between the railcard discounted Standard Anytime Day Single and the 1st Anytime Day Single (the student railcard does not have discounts for the flexible 1st Class fares remember), or the undiscounted Standard Anytime Day Single and the 1st Anytime Day Single?