Rapid Security Response

See >>> About the security content of Rapid Security Responses for iOS 16.5.1 and iPadOS 16.5.1 - Apple Support

RSR 16.5.1(c) is indeed current - being intended to mitigate a zero-day security vulnerability. The prior RSR 16.5.1(a) was withdrawn.

16.5.1(a) apparently had issues and was rescinded.

16.5.1(c) is the current version and installation IS recommended.

The “(a)” update was pulled. Now the “(c)” update is available as the improved version.