Check the delta mechanism in T. Code RSO2 (in source system) for any existing datasource.
Numeric pointer delta can be used : say any internally generated number range been used for transactional data records ( e.g. PLM document number) for for any new docs the delta pointer will take care for extraction, not sure how the change been captured (I guess thats the drawback of it)
Thank-You.
Regards,
VB