Apple now stops signing both iOS 10.3.3 and iOS 11.0 with the following release of iOS 11.0.1 and iOS 11.0.2 to public. That means user can no longer downgrade to iOS 10.3.3 or iOS 11.0.
If you want to restore or upgrade your iPhone/iPad from iTunes it will now automatically update your device to the latest version of iOS.
Downgrading to iOS 11.0/10.3.3 not possible
Those who have accidentally updated your device to iOS 11.0.1/11.0.2 via OTA or iTunes, downgrading back to iOS 10.3.3 or iOS 11.0 is not possible until you had a SHSH blobs saved for that. So it is impossible to downgrade your iPhone/iPad from iOS 11 to iOS 10.3.3.
Apple always gives older versions of iOS to restore whenever it releases a new version. So that people have ability to downgrade their devices to the previous version if they are not satisfied with the new one or any issues. But after some time, it stops signing the previous version and allow the latest iOS version.
You can also visit this link https://ipsw.me to check the signing status of Apple firmware.
Since iOS 11.1 beta is only available for developer testers, so for now the only two version ie; iOS 11.0.1 and iOS 11.0.2 are available for download and install on iPhone/iPad
by public.
