Apple is no longer signing iOS 17.1 forcing users to stay on iOS 17.1.1 and preventing further downgrades.
Apple stops signing iOS 17.0.3 preventing downgrades from iOS 17.1.
Following release of iOS 17.0.3 Apple stopped signing iOS 16.6.1 preventing future downgrades. The only previous release which is currently being signed is 17.0.2 (but developers should expect that this is not for long).
Downgrade from iOS 16.6.1 is no longer possible as Apple stopped signing iOS 16.6.
Following release of iOS 16.6 Apple no longer signs iOS 16.5.1 preventing downgrades.
Following the iOS 16.5.1 update Apple now stops signing iOS 16.5 preventing downgrades.
iOS 16.5.1 closes major security issues and therefore, it is expected that Apple will stop allowing users to downgrade to vulnerable releases.
Apple stops signing iOS and iPadOS 16.4.1 preventing downgrades.
In usual manner following iOS 16.2 release Apple now stops signing iOS 16.1.2 preventing downgrade.
Since iOS 16.1.2 release Apple no longer signs previous iOS releases preventing downgrades.
Apple now no longer signs iOS 16.0.3 essentially preventing downgrade from iOS 16.1.