First off, here’s a handy chart for reference. For something from 1946, you’d have to research the copyright to that specific film to find out if it’s been renewed. You could check with the company that released it, and that address can probably be found just by Googling the name of the company. If you don’t know the company, and can’t locate a legit copy of the movie to look at the box it’s in, it may be possible to find that information on AllMovie or IMDB. Hope this helps. :)