Instance and Duplicate Tag

I imported a lot of email and of course there are duplicates.
Over the course of trying to organize and clean up my emails, I played with the smart folders for finding instances where there are duplicates.

I have a few emails when I tell it to move ALL instances to trash, it only moves one message. This appears to mean that there is only one copy of the message. How do I reflag the message as being not duplicate? or is there a way to find the actual duplicate to this email?