Latest Firmware Files
Apple requires the latest signed firmware files
Normally when a new iOS is available, Apple will discontinue the last signed version within 1-2 weeks after the release of the latest iOS
Legacy Firmware Files
These are the devices that no longer support the latest iOS and need to be downloaded for these devices to be Restored.
Download all 9.3.5 files for iPad 2, iPhone 4, 4s
Download all 10.3.3 files for iPhone 5, 5c, & 5s
Download 6.1.6 for iPod Touch 4 & iPhone 3GS
Download 5.1.1 for iPod Touch 3G & iPad 1.
Download 4.2.1 for iPod Touch 2G & iPhone 3G
Download 1.1.5 for iPod Touch 1G