I think you cannot see the actual installed version of a plugin in the extension manager, unless you get the update message.
Anyway, the new refnotes release is out. See the date on the plugin page
https://www.dokuwiki.org/plugin:refnotes. If you are on the extension manager page make sure to clear your cache. E.g. go to the extension manager page and then append
&purge=true to the URL/address in your browser and hit return.
If you look into the filesystem, open the file
refnotes/plugin.info.txt to see the version.