The catalogue of movies and TV shows in Netflix changes regularly, depending on licensing deals Netflix has with the movie distributors.
New content is added all the time, but is removed less frequently. As a rule, Netflix usually removes content in bulk every 3 months. In the US, it releases a list of movies which are about to be removed as a last chance for customers to watch them.
JustWatch is a great tool for search the current Netflix database, as well as the catalogues of similar services like Stan, iTunes and Xbox Video.