The method used to get gnaf geocodes will return only a geocode that was matched to an address point.
This means that the geocode is for a single address or block of units.
Some records are marked as only being matched to the street or locality geocode, for example some rural addresses will have a geocode for their street but have yet to be matched to an address point.
When you have an address like this we recommend using the “DataTools.Enhance.Address.Geocoding.Gnaf.Au.Append” which has these street/locality geocodes.