Maybe you should reconsider Beta, because if you think about it is not a good release to run. Beta is like a release between Nightly and Stable, but kind of useless because while it gets updated often, it doesn’t get every change Nightly has quickly enough or at all until next ‘branch merge’, if there is a bug and it gets fixed (Nightly) then it will take days to go to Beta. so what’s the point?
You are not getting more stability or anything because Nightly uses Chromium beta releases so it is stable enough, because you are running the Chromium version that will be available in Stable 15 days after or so, so it should be already stable enough to run it daily.
All releases have Milestones and you can even check old ones, since it is like a ‘grouping’ feature for releases.
Obviously you click between open means it was pushed but not merged and closed means merged and available.
That’s how you do in Github, it would be a waste of time to write release notes for every release. Also, release notes are just Highlights, sometimes they don’t even mention many new fixes and stuff in Stable, from 300+ changes and only 30 lines of release notes, well, sometimes some good stuff will not be included. So the only way to truly see any change is by using Github milestones.