Toolbox version tracking

Yes, you are right. The download contains only the last major release. Minor updates are distributed by module updates within SNAP. Check the module manager.

Release notes
Releases · senbox-org/snap-engine (github.com)
Releases · senbox-org/snap-desktop (github.com)
Releases · senbox-org/s3tbx (github.com)

For the other toolboxes this is not available. We don’t have a consolidated way of posting the changes.

Usually, we also post here in the forum about updates:
SNAP 8.0.3 module update available - snap - STEP Forum (esa.int)