The USPS provides free Early Warning System (EWS) data to prevent matching errors due to the age of the address information in the .gsd files. The USPS creates a new EWS dataset each week that you may download from the USPS website (https://postalpro.usps.com/cass/EWS).
The USPS requires EWS files for CASS processing. You can use the use.gsd and usw.gsd files (located in the Spectrum Geocoding Data Package) for 135 days, but after 105 days you cannot create a CASS report.
When you download the EWS file, place the file in the same directory path as the .gsd data and make sure to name the file EWS.txt.