Setyl relies on a unique identifier to prevent duplicates being made when making bulk changes using the Bulk Upload feature. This unique identifier is the "URL" you will see when you export Assets from the Setyl platform. Every Asset created in Setyl is given a unique "URL".
As long as you do not change or edit the "URL" of the Assets you are re-uploading once having modified data, Setyl will not create duplicates of any of the Assets.
New Assets will only be created for any records that are uploaded without a recognised "URL".