I note you've made some changes. There is still some detail in there I'd be inclined to remove.
The parking operator cannot pursue you as the keeper as the NtK fails to meet the requirements of PoFA - specifically:
Paragraph 8(2)(a) - Failure to Specify the Period of Parking The NtK only lists a single moment in time rather than the actual period the vehicle was parked.
There are probably other failures to but my brain isn't working and it doesn't really matter at this stage.
Since you have missed the chance to appeal, you have two options:
1. Ignore the NtK and the likely debt collection letters to follow
2. Complain to the operator, including details of an appeal as follows:
PCN No: [PCN NUMBER]
Vehicle Registration Mark: [VRM]
I am the keeper of the vehicle and I dispute your 'parking charge'. I deny any liability or contractual agreement and I will be making a complaint about your predatory conduct to your client landowner.
As your Notice to Keeper (NtK) does not fully comply with ALL the requirements of PoFA 2012, you are unable to hold the keeper of the vehicle liable for the charge. Partial or even substantial compliance is not sufficient. There will be no admission as to who was driving and no inference or assumptions can be drawn. Open Parking has relied on contract law allegations of breach against the driver only.
The registered keeper cannot be presumed or inferred to have been the driver, nor pursued under some twisted interpretation of the law of agency. Your NtK can only hold the driver liable. You are urged to save us both a complete waste of time and cancel the PCN.
Any mitigating circumstances are irrelevant at this stage. And in your case, I don't imagine they'd get you anywhere in court either. The chances are it will never make it there and if they do, I would offer you a 99%+ chance of success if you follow the advice on this forum.
Rest assured that there is no risk of a CCJ. Even if it proceeds to court - so long as you pay you will have no issues.