Updating contacts by exporting to excel and reimporting

I am looking for a method to mass update contact records.  I understand that CRM 2016 should be able to update records by importing the data from excel with the de-dupe switched on.  However, I have met no success.  The import logs show partial success and indicate the records have been updated.  However, when I review the data, nothing has changed.

I have read posts that mention the reimport option, but can not see that on the export process.

Any ideas what I am missing? 

Thanks!