"The Korea Postal code system changed from a 6-digit postal code system to a 5-digit postal code system on August 1, 2015" (source). So if you look up for example the old "korea 110-744" or "korea 110744" on Google Maps or GeoNames.org, you draw a blank. But if you simply Google it, you do find references to gazetteer websites, such as http://south-korea.postcode.info/p/110-744.
Is there a good (ideally open) source of structured (machine-readable) geolocation (address and ideally long-lat) data for South Korea pre-reform postcodes (and ideally current ones as well)? The address could be romanised or in hangul, but that would be indifferent if long-lat is provided. The goal is to geolocate (long-lat) a dataset of addresses going back to the 1980s.