USPS Zip Code polygon Database Update Policy
USPS Zip Code Polygon Database product license policy is as follows:
The database has a "perpetual" license which means that the license doesn't expire.
The license covers the release of the database that is current when the license is purchased.
Future releases of the database must be relicensed at the then current price.
The database is released up to twice a year (two versions), usually in March (January data) and September (July data).