Netflix is a creature in constant flux, always adding content to hook in prospective subscribers. But to make room for the fresh stuff, some of the stuff you’ve always wanted to watch—and have had in your to-watch list for months or years—has to go to a farm upstate, never to be seen again.That’s because Netflix doesn’t own all the content it streams. The contracts it has with networks, production companies, and movie studios mean much of that content comes and goes with startling regularity. So each month, we keep you…