Missing change notes (in CHANGELOG.md) for some Swift releases?

Swift source code repo has branches 5.9, 5.9.0, 5.9.1 and 5.10. But its CHANGELOG.md has only change notes for 5.9, 5.9.2, and 5.11. I wonder why the mismatch? Are 5.9.1 and 5.10 internal releases so they don't have release notes?

P.S. I noticed the above when I tried to figure out what Swift and SwiftUI changes Xcode 15.2 contained without installing it. As far as I can tell, Xcode release notes has never contained such information. It just included the SDK version, but I can't find more detailed information about what the SDK includes.