The list of colour-coded routes and Train Operators looks pretty clear to me!
The fact the railcard is valid as far as Stafford is very clear. The bit that
isn't clear is that it is only valid on LNR and not on Avanti. For that you have to look at the key and twig that LNR is not Avanti and that the absence of Avanti means it's not valid with them.
That's a lot of mental gymnastics compared to, say, a sentence on the National Rail website under the section 'where can I use my annual gold card' which states NOT VALID ON AVANTI OR LNER.
And that's before we consider this little gem:
Image shows extract from the Annual Gold Card map.
The text box saying "gold card is valid on all National Rail services within this area" is placed across both the white area (outside the London zones) and the yellow area (inside the London zones). So which one does it apply to? And how do you know unless you know?
In trying to defend this, one can only presume you are borderline trolling tbh.
Of course, if the map is so clear then that rather undermines your other point. If the communication is so completely clear, why didn't the staff member know?