As I understand it, MC uses themoviedb.org for Movie lookups and thetvdb.com for TV show lookups. The movie you mention, Conan The Barbarian is a favorite of mine. Well, the 1982 version, not the newer 2011 version. I just did some searches and I can't find anything called "Conan the Barbarian Director's Cut".
Maybe you have "the complete quest", which includes both CTB and Conan The Destroyer?
In any case, it really doesn't matter. Because the various releases of DVDs (and BDs) don't really have different database entries. The database entries describe the film in general: The cast, description, budget, rating, keywords, etc. The different releases don't change from that perspective.
You can certainly do your lookup with the base name (like Conan The Barbarian), and then change the title after to whatever you want, to annotate the actual DVD release that it came from. Then you'll have the best of both worlds: A proper description (and other metadata) and the title you want shown.
Brian.