Could this be the iPhone manufacturing date? Go to settings/Cellular then scroll all the way down to the very bottom. It will say last reset: Sep 19,2013,8:08 AM or what ever your date is. This is not from a previous back up. it was like this before ever connecting to a computer, and I checked around 10 of them at the Apple Store and they all had dates in September. Check it out and post back please!