Do you take 9-digit ZIP Codes as input?
Does the Smarty (formerly SmartyStreets) LiveAddress API take 9-digit ZIP Code as an input parameter?
Smarty will accept either a 5- or 9-digit ZIP Code as input, along with the relevent address info but we always regenerate the 9-digit ZIP Code. The reason for this is that the postal service is constantly realigning ZIP Codes. Obviously, a building or a house doesn't change it's physical location but the street name and ZIP Code are subject to change. Of the 42k ZIP Codes in the US, approximately 4% of them are changed in some way each month. This could be due to an enlarging or shrinking of the ZIP Code area. A ZIP Code is merely a delivery area designed by the postal service for convenience and efficiency. They change it any time they want. The USPS is constantly opening, moving, and closing offices. This means significant changes to the ZIP Code structure.
So, if you enter an address with a 9-digit ZIP Code and the post office has changed the 9-digit ZIP for that address, we will output the corrected address and 9-digit ZIP.