I'm not sure what nostra's plans for version 1, but this has been discussed before. In Preferences>Miscellaneous, there are options for applying checks to adding records. The problem is, these don't work very well and, in practice, are a PITA. I leave them off, and accept the consequences. The duplication is easily fixed by updating the record. Unfortunately, updating the person can also change their appearance in the movie record—so it needs to be updated too.
So a better way of doing is called for, but an effective solution is probably more complicated than you think. I can't remember the details, but when I thought this through before I came to the conclusion it would probably require a change to the architecture of the database. Not only would that mean a lot of work for nostra, chances of the new version being able to properly convert existing databases might be slim.
