‘Signing’ is what allows a device to go back to a previous iOS version (Apple’s servers sign off permission to install each software version) and is commonly used when a user experiences trouble with new software version. Consequently with the release of iOS 9.0.2 Apple has taken away the escape route back to iOS 8. It’s iOS 9.0.1 and 9.0.2 now or nothing.
It would also be unprecedented for Apple to put out four iOS updates in such quick succession (three in itself is new ground with Apple last doing two only when it had to release iOS 8.0.2 to cover for pulling the troubled iOS 8.0.1 from the market). And what about losing the sign off for iOS 9? That actually matters far less since iOS 9.0.1 (still being signed) and iOS 9.0.2 are both tweaked improvements of it. Basically if you are struggling with iOS 9.0.1 or iOS 9.0.2 then iOS 9 is not going to help you – though a trip back to iOS 8.4.1 (the final version of iOS 8) would have.