People will buy the rights to movie ideas and then do nothing for years or decades. Sometimes they buy the rights "just in case". "It's official" means little. Signing for film rights gets announced, nothing happens, then something comes out of nowhere and gets made without fanfare, right? I think. "It's only official" might make more sense.
You can't even go by whether they announce a show's been canceled or picked up. I've noticed those announcements getting reversed a lot in recent years.