Clearwell tagging question for Predictive coding

We have a question on how PC (Predictive Coding) will handle the analysis if an email body is not privileged but one of the earlier/later replies or forwards is privileged...

All messages are indexed (no derived emails) so I believe each email would then be tagged on its own merit, and the prediction will be based on each email and not on the entire thread. What are the thoughts on this from the community?

Also, how would this be handled if some of the messages are derived?

Thanks for any thoughts/comments.