Missing Compensation Zone by location

Summary:

We have compensation zones / differential profiles set-up in our production environment and find that there are several locations where the zone is missing. After running the Generate Compensation Zone and Address Mapping (purge) , logs simply say 'WARNING No Zone found for this Location/Person.'

What is strange is that for two locations; in the same city, for one city the system shows the zone correctly and for a second location in same city the zone is not found.

The locations are active; they have complete and accurate addresses and the postal code / city etc. is all active and correct in teh Manage Geographies Hierarchy. I can find no inconsistency between the set-ups.