We autoenter counties from the zip file and it works correctly (most of the time). NY is the land overlapping political jurisdictions. There are zip codes that cover parts of Westchester County and the Bronx. Worse yet they have different sales tax rates so you can't even compute taxes from the zip code. There are also towns in NY with CT zip codes, again nasty in a sales tax situation. Multiple town names with the same zip code are common, worse yet frequently one or more have a snob appeal compared with the others. There are also (mostly snob reasons) postoffice non-preferred names that people use when they send you their address. You have to make some set of policy decisions and stick with them. Mostly the postoffice is amazing at what they will tolerate and recover from. While in graduate school I got (in only two days), mail to me at Two Lane Drive, Hyattsville IN (no zip) when my real address was Tulane Drive, Hyattsville MD.
