Changelog
What shipped, and when
One page per plugin, each one generated from the release record the update server reads. Nothing on these pages is typed out by a human twice, which is the only way a changelog and the software it describes stay in agreement.
By plugin
No release history available
The release history could not be read when this page was built. That is our problem rather than yours, and the next deploy will pick it up.
How this page is built
Read from the release record
Each entry is a row in the same table the WordPress update check reads. A release that is staged but not published is invisible here, exactly as it is invisible to wp-admin, and the version list is ordered by semantic version rather than by date — so a patch backported to an older line files itself under that line instead of jumping to the top.
Beta releases are labelled. They are only ever offered to sites that have opted in, never to a site on the stable channel.