[LogicHoleFlaw]

Speaking from experience... apartment numbers are one of the most difficult things to process correctly when geocoding, particularly if your service is backed by Google. The experience you describe sounds exactly like someone didn't correctly handle the edge cases surrounding subunit numbers.

I spent quite some time banging my head against these issues for a former employer. Lots of trial-and-error was employed to build up a basket of test cases around apartments. Certain addresses remained intractable.