Once other variants of the Samsung GALAXY Nexus receive Android 4.1.2, those models will also receive a Factory Image. In the meantime, you should just file this information somewhere in your head where it can be retrieved if needed. If you do ever need to use the Factory Image, you should remember that just like at home when you lock the door after you leave to prevent the bad guys from breaking in, after restoring the firmware on your phone you need to lock the bootloader. Also, the operation will remove all user data from your phone or tablet. At least your device won't be a brick!
Factory Images for Android 4.1.2 are available for the Google Nexus 7 and a certain variant of the Samsung GALAXY Nexus