What I cannot understand is why one has no access to the informal representations made.
It's a moving traffic case so there are only formal representations, there is no informal stage. As they're your representations, one could say that it's up to you to retain a copy for your own records, that being said most authorities will provide a copy if you ask (but doing so does not pause any timelines).
One thing: If I still had the option of the discount, would you recommend paying it at the discounted rate?
Yes, I can't say that there is anything I can see that would warrant risking the full amount and I infer that the access provision is not relevant or else you would have said so by now.
That being said, the penalty can't go up if you appeal so I suppose you might as well put your case to the adjudicator. I'm just not sure what you'd base your appeal on at present, but there's nothing to stop you simply putting the authority to proof.