In December 2015, Star Wars: The Force Awakens was released in theaters with a massive following, netting over 2 billions dollars at the end of its theater run. There was a noticeable difference between this film and what came before it— George Lucas had a minimal involvement with the film. This begs the question of whether or not, despite its popularity, the movie and any subsequent movies can be considered canon. While I will use this post to focus on Star Wars and the subject of continuity, the subject is too broad to put into one post.
The Prequels, despite their reception, are only begrudgingly accepted by the general fandom. Also, they accept that there’s a multitude of characters and details which they both love and hate about them, such as Darth Maul and Jar Jar Binks. Overall, the material brought by them was a net improvement to the Star Wars continuity, in my opinion.
On April 25, 2014, Lucasfilm declared that the Expanded Universe would be rebranded under the name “Star Wars Legends”. This made nearly 40 years worth of lore “non-canon”, in order to make way for the story for the new movie trilogy, as well as other material. Personally, I consider Legends to be an alternative universe for the series, as I believe that is too much work from fans to be considered irrelevant. The fans who were more involved with the Star Wars lore generally enjoyed the stories which were created during this time as well.
At the end of the day, I believe that the fans of a particular series declare a consensus on what is considered “Canon” for a series. For example, despite Lucas’ lack of involvement with The Force Awakens, the fans accept it. On the other hand, it’s extremely rare to see someone who accepts, or acknowledges, that the Star Wars Holiday Special is part of the lore even with George Lucas behind the story. (Lucas apparently declared the special to be non-canon himself). The series could be considered to be a living thing, to form and shift as time goes on, even going so far as to rot and die if left to do so by the passage of time.