... I've generally made a point of adding not:addr:postcode=* when I came across an incorrect postcode in the FHRS data. If others did the same, the comparison tool ... could presumably make use of such tags and provide a list of postcode errors for each district. (It could also use the presence of such a tag to suppress/de-emphasize the postcode mismatch errors it reports.)
On the mailing list, Robert Whittaker writes: