So, what Alien: Earth is saying is Weyland-Yutani is aware of xenomorphs (among other creatures) well before the events of the films and was *this close* to getting one back to Earth.

In the US, Hulu offers every single one of the movies, so it should be your one-stop shop. It's also where Alien: Earth will land. A subscription starts at $9.99 but there are sometimes Hulu deals.

Alien: Earth takes place just two years prior to the events of the original 1979 film and centers around Wendy, a groundbreaking human-synthetic hybrid whose consciousness was transferred into an android body to save her from a fatal illness.