@msmurfitt for the Google Play releases, once you release the track, the user just needs to go back to Play Store link, and they can update from there! So the same link to your app in the Play Store will work for every release.
If your users have their device set to auto update apps, it will just update to the newest release when the device recognizes a release is available.
This has been my experience with the internal test tracks. You don’t need a new link, or to invite users to new releases as they are published to each test track. This is because the user is a member of the test track, not the specific release.