Email threading is performed in order to avoid the need to read the separate parts of long email threads over and over again.
Relativity defines inclusive emails as those which must be reviewed- they include all of the content for a thread. Non-inclusive emails do not need to be reviewed - but note that the threading analysis does not take the email headers into account.
Duplicate spares are emails which contain the same content as other emails and so do not need to be reviewed.
DRAFT emails are an anomaly. Draft messages are never treated as duplicate spares. They will always be marked as inclusive, and be considered unique content.
Draft emails have this icon with a pencil in the email threading visualization:
So if you have these added to a review don’t think it means they were never sent!