I have to check the Netflix New Releases on HackingNetflix.com, because I love rating the ones I've seen. Occasionally, one will show up that I have previously rated! It went out of print, and then came back. Or maybe I saw it in the theatre and rated it before it was available. Or maybe I rented it from Facets or Greencine. It's how I keep track of what I've seen, to improve recommendations.