I think I would want the guide data to show first run even if it was on a different US channel for the first time in syndication. I don't get UK channels and the show is as brand new to me as the Soprano's were to those who did not get HBO when they started airing that series on national tv.
I obviously have been missing Primeval and Continuum and did not know it until this thread. How much have I missed?
Setting a first run flag is quite different than what others have suggested, changing the first aired date. A first run flag should be present, I agree.