Free Traffic Legal Advice

Ignore.

Ignore debt collectors, who are powerless and will use scary words and red ink.

Your wife should have previously received a Notice to Keeper from APCOA. Is the car's V5C up to date? There is a simple response to the PCN which would have seen APCOA cancel.

In any case, APCOA do not "do" court. Ignore debt collectors and only if APCOA change their modus operandi, come back if you get a Letter of Claim from a solicitor.

It possible / probable the NTK went to the original lease co, depending on dates.  Probably best to submit a Data Rectification Notice to APCOA advising them of the current address for service and instructing them to update their records and to delete any previous address.  Refer only the PCN reference number and as keeper.  Last thing you want is for APCOA to go to court (should they change MO!) with the wrong address and it gets missed because it goes somewhere else.  No keeper liability on the airport so there is a defence if needed - as long as you don't reveal the driver's identity!  No harm in submitting a complaint (as keeper!) that you didn't get the original NTK, that there is no keeper liability due to airport, and inviting them to cancel it.  APCOA often roll over when confronted with this.