Furthermore, searching for those extra postal codes that appear in the web search for "somersham" in the allCountries.zip results yields no results. So they are clearly missing from allCountries.zip file for postal codes.
Where can I download ALL the GeoNames postal codes that includes the COMPLETE set of postal codes as reflected in the web search tool?
At the moment GB is the only country with a large additional dataset.
NL will probably be next. Reason is that the granularity and size of these datasets is at least an order of magnitude different from the others: city coordinates vs block coordinates.