You need to appeal each PCN separately. What you have suggested writing is fine. However, I doubt they will “reset the clock”.
You must remember that you are dealing with a, mostly, automated money making machine. Any human involvement/intervention is likely to be by someone who is intellectually malnourished and incapable of understanding the minutiae of your arguments.
Regarding the status of the location, you seem reluctant to accept that it is National Rail railway asset, leased by the TOC, Abelio Greater Anglia and operated on a commercial basis by NCP. None of that detracts from the fact that, as a railway asset, it is covered by bylaws, whether there are signs there or not.
It is not relevant land for the purposes of PoFA and, as such, only the driver can be liable for any alleged breach of contract. Keep that in mind whether they accept your allegation that they never sent the original NtKs.
Consider your correspondence as a complaint rather than an appeal. The reason for that is, should they not reset the clock which would allow you to appeal to POPLA, you are then in a position to complain to the BPA regarding their breach of rule 23.8 of the current BPA CoP.
Should none of the above work, you are then in the limbo state of waiting to see if they try to make a claim. You would receive a flurry of debt collector letters which you can safely ignore. If/when they send you an LoC which you can respond to, robustly, you will again be in a position to argue that you cannot be liable as the keeper and to bring on the claim.
Whilst they may never get to this stage, there is still the possibility, because of their intellectual malnourishment, that they will issue a claim in their greedy hope that you are gullible enough to capitulate and pay up. Defending any claim robustly is very likely to lead to a discontinuation because they really don’t want a judge to spank them in court.
