If I have understand correctly you have for example a tv show, LOST.
You have import all your episodes from your Hard Disk (I mean that all episodes are "linked" directly with movies in your hard disk).
Now you want know what episodes are missing, right?
What I suggest is to :
Import ALL Episode info from internet about LOST.
The Episode that you have in your hard disk have the field "moviefile1" with the link to file.
Simply show in the Episode Grid the Field "moviefile1": now you are able to see what episode of LOST you have in your hard disk and the episodes you haven't.