Documents that are imported as part of a batch belonging to a scan queue configured to use the Append to Existing Documents Matched on Keyword(s) scan queue setting and are indexed via Advanced Capture(either batch or ad hoc Advanced Capture) are appended to existing documents with the same Document Type and Keyword Values.
See the Document Imaging module reference guide or help file for more information on the Append to Existing Documents Matched on Keyword(s) scan queue setting.