In the 1990s, during the runup to the Star Wars prequels, George Lucas released the special editions of the Star Wars original trilogy. Since then, multiple versions of the OT special editions, as well as prequels, have received DVD/Blu-Ray releases—but not the OT theatrical cuts. In 2012, Lucas sold Lucasfilm to Disney, which decanonized the Expanded Universe and called on Chuck Wendig to write three books to bridge the OT and sequel trilogy. They also scrapped Lucas's notes and script treatments for the ST. For 8 years Kathleen Kennedy has run Lucasfilm and Star Wars, some say (myself included) into the ground.
More people have seen Blade Runner than read Philip K Dick's Do Androids Dream of Electric Sheep? In the book Deckard takes a Voight-Kampff test and passes; therefore, he's not a replicant. The movie's original cut is ambiguous at best, but Ridley Scott's director's cut hints strongly that Deckard is a replicant. Scott has come out and said that's the case, no two ways about it. But Blade Runner 2049, produced by Scott, omits this certainty and embraces ambiguity.
JK Rowling's writing style matured along with her core audience through the late 90s and 2000s. Book and movie ticket sales lifted her from poverty to the most read author in the world. Since the 7-book Harry Potter series concluded, she's maintained Dumbledore is gay, something that's yet to be shown in any of the actual books and movies.
The Wachowski Brothers became the Wachowski Sisters years after the Matrix trilogy came out. Lana Wachowski (formerly Larry) now claims the movies are a trans allegory, not a reimagined allegory of the cave like we all thought at the time. You may assume the trans allegory will be the operating ethos of the upcoming fourth movie. It's unclear how breaking free from machine-induced mind control aligns with using medical technology to posit the will over reality, but what do I know?
I claim ignorance about all things Trek, but more TV and movie content has been produced after Gene Roddenberry's death than before. There's been an alternate timeline with two different Spocks, and a weird IP split that I still don't understand.
The problems with most of these franchises revolves around the legitimacy of canon. What is it, and who defines it?
Is it defined by quality, continuity, consistency, or all three? Is it defined by the IP owner? In Star Wars's case, that would be Disney, who say that Anakin Skywalker didn't kill Emperor Palpatine, and that Luke Skywalker abandoned his friends in their time of need. Or is it defined by the IP creator? Again, in Star Wars's case, that would be George Lucas, who said in 1977 Han shot Greedo first but who maintains for the last 23 years that he hasn't. Is he allowed to change what happened decades after we experienced the story a hundred times over in our imaginations?
"To me, [the original movie] doesn't really exist anymore. ... I'm sorry you saw half a completed film and fell in love with it. But I want it to be the way I want it to be." -George Lucas
For fans, these discussions are not superfluous. Movies and books are content, and what do fans fall in love with but the content? Retcon the content, and you test the fans' suspension of disbelief. It's not all that different from a Christian losing his faith after marrying another Christian. At the very least, it strains the marriage.
I'm not really involved in fandom. I never was. Star Wars mattered the most to me, but now I refuse to care. Nevertheless, Lucas, Rowling, and the Wachowskis have forced me to take the position that even the creators of these IPs can't be trusted to define canon. Creators aren't static, and the successful ones are frequently vain. They change their minds. Are fans supposed to change as well?
For me, canon is the art's content in its original form. Han shot first, Deckard isn't a replicant, and Dumbledore isn't gay. (As someone who saw the director's cut of Blade Runner first, the second statement of these three has been the hardest to accept.) Fans who contend otherwise must reckon with how the creators told their stories the first time. Were they wrong? Even taking into account the compromises inherent in the creative process, I'm not prepared to say they were.
As always, let me know what you think in the comments. If you like hard sci-fi, check out my books Seeds of Calamity and Tendrils to the Moon. You can find extended previews for each here and here.