You first have to ask why you never received the original PCN. Is the V5C up to date with your current address? In the vast majority of these cases, after changing address, the Keeper updates their drivers licence with the DVLA which does not automatically update the V5C. Go check now. If it isn’t, you need to update it immediately as you could receive a real fine from the DVLA.
The reason DRP+ found your address is through a credit reference agency. If the address APCOA holds is an incorrect one from the V5C, you MUST send a data rectification notice to the APCOA DPO instructing them to update their records with your correct address for service and to erase your old address. Not doing this is and leaving APCOA with two possible addresses for you is a surefire way to get a CCJ by default.
No one who is here receiving advice pays a penny to APCOA. This would have been so easy to deal with at the time if you, the Keeper, had simply appealed with the following:
I am the registered keeper. APCOA cannot hold a registered keeper liable for any alleged contravention on land that is under statutory control. As a matter of fact and law, APCOA will be well aware that they cannot use the PoFA provisions because Luton Airport is not 'relevant land'.
If Luton Airport wanted to hold owners or keepers liable under Airport Bylaws, that would be within the landowner's gift and another matter entirely. However, not only is that not pleaded, it is also not legally possible because APCOA is not the Airport owner and your 'parking charge' is not and never attempts to be a penalty. It is created for APCOA's own profit (as opposed to a bylaws penalty that goes to the public purse) and NCP 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. APCOA have no hope at POPLA, so you are urged to save us both a complete waste of time and cancel the PCN.
However, you are past any appeals deadlines. Luckily for you, APCOA are benign, in that they do not litigate. If you ignore the useless debt collector letters, and we do not need to see them either, they will eventually stop and that wil be the end of it. If you feel the urge to be proactive, you could send a formal complaint to APCOA, basically saying what is in the suggested appeal above and they are bound to consider it as an appeal anyway according to their Code of Practice.
Either way, they will not litigate. However, there is no guarantee that you’ll not be be the first person they try, and if they hold an out of date address for you, you’d guarantee a CCJ. Get your V5C updated.