The Migrate screen has been enhanced to show updated migration statuses on the Migrate Existing page.
This helps users easily identify files that have already been migrated. You can view these details in the ‘Migration Status’ column. 


PS: View Drag, Drop & Upload Files to Amazon S3, a Salesforce AppExchange app for moving files from Salesforce to Amazon S3: https://appexchange.salesforce.com/appxListingDetail?listingId=a0N3000000B5ZPqEAN