If there's an error in the CSV file, such as using file names that don't match existing files, you'll see an error message in the status column when you upload the CSV. This message tells you that the file name you provided wasn't found in the uploaded CSV. This helps you notice and correct any errors in the file names so you can upload files successfully.
PS: View Mass File Upload, Salesforce file upload app, on Salesforce AppExchange:
https://appexchange.salesforce.com/appxListingDetail?listingId=82cf236b-1ee8-4ea7-aebf-fd0c89fb93bd