Do talk about the anomoly of using postcodes as informal internal keys to "unknown " so e.g. a small community in the northwest of scotland or shetland or somet

Do talk about the anomoly of using postcodes as informal internal keys to "unknown " so e.g. a small community in the northwest of scotland or shetland or something has an astronomically huge unpaid VAT bill because how people were tagging "no data" in their processing. (I can't remember the full details, but its similar to the lake in the centre of the USA which people keep GPS driving to)