Many of the movies that get 4K Cinematic updates are also getting updates to the regular 4K versions, because it's an opportunity to revisit those movies with our latest encode recipes and tools while we have the mezzanine assets unarchived. However, if the movie is a relatively recent release, it may already have been processed with the latest tools, in which case there would be no benefit to doing it again.
Regarding how updates work: you'll get a notice for updates to the version of the movie that is on your system. For the standalone players, that means that in practice, you won't get very many such notices, since there aren't many movies on the system at any one time. The next time you download the movie, you'll get the newest version, of course.