I see what you mean now.
My work around is this - I have the sub tags "Movie" and "TV Show" automatically applied to all files going into specific folders, then after Carnac has looked up the meta data I go back and change the sub tag as needed. So if I record the TV Show NOVA it goes into recording folder "TV Recordings" and everything in that folder gets media sub type "TV Show" automatically applied. Carnac does its thing. Later when I do my "maintenance" I move the TV Shows to their permanent folders and update the tags if needed (so in this example, I change sub tag TV Show to Educational for NOVA).
It's not a perfect system but we have to work with what we have.
Maybe, in a future version, JRiver good allow one to select what Internet lookup source to use for each sub type. Then you could selectively assign media sub types "TV Show, Educational, whatever" to use TVDB and "Movies, Music Video, etc." to use IMDB or such.