Good to know!  Is the method documented anywhere?  I'm asking because I've been adding lots of housenumbers just north of here, mainly from out-of-copyright NLS-hosted maps and from lots of direct in-person surveys for postwar buildings and edge cases.   I've been adding postcodes to the centre-most building of each postcode only, from Code-point Open.   (So once you hit E15 / E6 / E13 etc, you'll come across these entries.)

Happy to help, or to leave you to it!