You can try setting the filename as DocID. Now with this the documents to be inserted will have a unique ID associated with them.
So in the next turn you can use
index.refresh_ref_docs
to add. It will not change the previous records if they are same and will only change the nodes which have changes in it or are completely new.
You can check Document management here for more:
https://docs.llamaindex.ai/en/stable/module_guides/indexing/document_management.html#refresh