> The upshot of the research then, is that building an accurate database is really hard. OS concludes that it would have to check the 4.2m bad addresses manually to make its PAF-less database a viable dataset that would actually be useful.

The secret to the Royal Mail's success with the PAF, and the reason why only the Royal Mail can maintain the PAF, is that the Royal Mail has people walking and driving to all those delivery points six days every week.

Compare the Freedom of Information requests to Royal Mail from OpenStreetMap contributors concerning the locations of post boxes, which were refused ultimately because that information was handled only by local sorting offices.