Check other libraries in iTunes. Any you've dragged into iTunes is probably in there now, but maybe under "movies" or "TV Shows" or something else. In short, video files are typically tagged as some kind of playback file: "home movies", "movies", "tv shows" etc. Tags are not set based on dragging them into a screen. My guess is that you'll find the ones you've already tried to drop into "home movies" in the "movies" screen, but they may be in one of the other sections too.
If you punch in the name of the movie in the "Search" field, it will likely show you in which category it's located.
If they are not showing up in iTunes at all, I'd start wondering about the format of the files: is it one of the video file formats iTunes supports?