Aside from the occasional legal quirks and roadblocks, owning a Nexus device is great because you’ll always have access to factory images of your device in case you ever need to completely undo any customization or just want to start from scratch. If you happen to own a Nexus 4, 7, 10, or a GSM Galaxy Nexus, you’ll now have access to those factory images for the latest version of Google’s Android 4.3.
The Nexus 4, all older versions of the Nexus 7, the Nexus 10 and the Galaxy Nexus all have images with the build number JWR66Y. The new 2013 Nexus 7 has a different build number, build JSS15Q, but still serves the same purpose. If you’re looking for any CDMA variants of any Nexus devices, you’re unfortunately still out of luck.
source: Google Developers