I haven't found a way to get the original file, but you can view spreadsheets imported in
Settings -> Data Management -> Imports (change view to All Imports). From there, you see the individual records that were Created/Updated.
If you have access to the database (on-prem only), you can query that data via SQL:
SELECT id.importfileidname,
id.linenumber,
id.data,
id.createdbyname,
id.createdon
FROM importdata id
WHERE id.createdon BETWEEN '9/22/2014' AND '9/24/2014'