FAQ What does the value of "W" mean in the Address Error field in Address Check? The value of "W" means that this address was found in the USPS Early Warning System (EWS) .  The EWS file includes addresses that will be added to the USPS ZIP+4 Code master file in the coming months, such as housing developments and new construction.  EWS ensures that addresses not on the USPS master file will not be eliminated or coded inaccurately. The USPS updates their EWS file weekly. To get the most current EWS file, click the "Download latest EWS File" button in the Address Check options screen before you run Address Check.  You will need and Internet connection for this to operate.  It is recommend you check for EWS file update every week to ensure that you have the latest data.