Sorry to be a PITA, but can you please post-up the PCN, all sides, so we can check it for fatal errors.
Your case comes under what is called a "driveway", whereby a CEO sees a car in apparent contravention, so starts preparing a PCN using his hand-held terminal. However, before it can be served to driver or car, the driver drives off. In such circumstances, the council can serve a postal PCN.