My, correctly issued, excess was as follows:....
To say it is 'correct' implies you have documented proof that it is, despite staff on this forum not being aware of it. The excess fares section of 'the manual' does not allow for this type of 'excess', therefore, IMO, your ticket was incorrectly issued.
The conditions of the railcard itself state that if you travel on a discounted ticket without the railcard you will need to buy a new ticket, and never once says you can change it beforehand for anything else. The NCoC simply says that a railcard discounted ticket must be accompanied by the railcard.
....I was told that it was possible to excess it to a non-discounted fare (it is not possible to change the discount, although this can be done if a manager authorises it, as I am aware that someone changed a 16-25 discount to a disabled discount last Summer, on an Advance ticket, with no admin fee, but this did require authorisation by a manager to do that. A straightforward excess can be done by competent ticket office staff)....
Out of interest, who told you it could be done?
I have never seen a manager authorise an excess outside of the rules, atleast not in an official capacity. I personally believe that if the discount is the same, there is no real need to excess the fare (discretion should be used).
....It can be done and my advice to the OP is to ask for it, state it can be done and that you have spoken to someone who got one! If they refuse, keep shopping around until you find a co-operative and knowledgeable ticket clerk....
A competent clerk that doesn't know the rules? Tricky. Do you actually mean "shop around until you get what you want"?
...I refuse to accept First Class's claim that it is either 'not allowed' or an admin fee is applicable, and even GNER agreed. And you know what GNER were like for sticking to the rules!
Well that makes a change (sarcasm). Previous threads show that what CAN happen and what SHOULD happen are not the same thing. Nowhere in Excess fares does it say it CAN happen, but nothing is actually stopping staff from doing it.
When you say "GNER agreed", do you actually mean "a member of GNER ticket office staff agreed"? There is a difference.