CalDAV/CardDAV server behavior after restoring to an old version

Question

Assume the following situation:

• A CalDAV/CardDAV server is used by different clients.
• Each of the clients keeps data locally and synchronizes periodically.
• The server goes down and is restored from an older backup.
• Clients had made local changes and synchronized them to the server after that backup was taken, so the restored server does not know about them. This can include addition of new entries, changes to entries synced before the backup (so the restored server would have an older version) and deletion of entries.

What would happen to changes made after the last backup?

• Would clients simply re-sync any updates to the server?
• Or would clients keep those changes locally but never synchronize them to the server (assuming the server already has them) unless there are further changes?
• Or would the server undo all changes made on clients after the last backup?
• Or is the transport protocol totally agnostic about this, leaving it up to the client and server how they deal with this?

If products matter, the particular setup I am interested in is a DAViCal server with one client running DAVx⁵ on Android, the other running Thunderbird for Linux with CardBook and Lightning extensions.