While in G Suite you have the ability to view the revision history of a document within the document itself. If you export the document out of the Google account and download it locally, you'll notice that Google does not include the revision history in the exported file. Since Google does not include the revision history during the export process, we're not able to back up or restore that data.
However, you do have the option of restoring an older version of a backed-up document by choosing an older backup date/set from the "Restore" page in your Spanning Backup account.