Also the Barthesian framing of "accessing intention as fruitless," is true, but only inasmuch as the imperative of understanding authorial intent fosters an elitism, an intellectual-smugness, and an exclusionary attitude towards the non-literati among academics and critics. If you create an environment wherein only those with highly specialized knowledge and jargon, and with access to materials for the pursuit of biographical research can truly access the veritable "meaning" of a text, you've instilled a hierarchy of critique wherein only a select few are allowed to hand down "the official reading" from on high. Barthes's project, at least in part, was to restore the tools of criticism to the people.
Also Death of the Author emphasizes the very critical point that the artistic process is not a one-way street, nor does it complete at the point of production/publication. The auteur in the abstract might have had some kind of "intent," or larger metameaning, but that metameaning is pointless absent the presence of its receptive audience. If you only read the core texts of Harry Potter, and interpret Dumbledore's reluctance to confront Grindelwald as rooted in his deep-seated guilt over the death of his sister, and his uncertainty over just who cast the curse that killed Ariana, and the larger fear that Grindelwald did possess that knowledge and would deploy it to defeat Dumbledore, would that interpretation be invalidated by Rowling's revelation that actually Dumbledore was gay, and in love with Grindelwald? Would it be invalidated by Fantastic Beasts 2, in which it is revealed that Dumbledore made a blood pact with Grindelwald that physically prevents him from confronting Grindelwald? Is the correctness of your interpretation false for all time unless you read Rowling's press conference, and unless you see Fantastic Beasts 2? Does this mean that your interpretation of the books prior to learning this information invalid, and can never be validated unless Rowling releases this information? If you enjoyed that component of the original 7 books, is that enjoyment invalid absent that information? If you don't like Rowling's subsequent revelations about Dumbledore's character, does that mean that your dissatisfaction is now rendered invalid? Are you not allowed to retroactively dislike the book? These are some of the core tensions that rest at the heart of Barthes's critique in "Death of the Author," both in the form of enjoyment and interpretation only being valid when viewed through one, singular "correct" lens, and in the implication that a correct interpretation can be achieved only when one accesses ALL of the information necessary for such an interpretation. If the goal of consuming art is to achieve a perfect understanding of an author's intent, then suddenly, reading and enjoying Harry Potter is only possible, not just after reading all seven books, but also reading all of Rowling's press conferences, reading all of her Pottermore entries, watching/reading the Cursed Child, watching all the Fantastic Beasts movies, and waiting endlessly in the event that Rowling might release further details that will eventually invalidate previous information, and even then, maybe she never reveals those details, maybe she never writes them down, maybe there's some slight detail that only Rowling will know, and which she'll take to her grave, which completely invalidates any thought you might have on Dumbledore and his motivations prior to that never-to-come revelation. What's the point of reading the books at all, then?
Also there's the uncertainty about Rowling and her statements. Rowling might say that she always wrote Dumbledore knowing that he was gay, but how do you know that? How does she know that? Rowling can only ever comment on what she thought she was thinking at that time, and even then, her commentary is inevitably going to be colored by the cultural climate, by audience reactions, and by her own subsequent personal life experiences. Trying to get at "what an author intended" and "what an author knew," is always going to be a project in chasing a phantom, and will always be read as the capital A-Author's word through the lower-case-a author's word, through your own interpretation of the former two, through your own lens and biases. If J.K. Rowling says she intended Nagini to actually be a cursed Indonesian lady from day 1, do you take that as Word of God and assume it to be true? Do you read it cynically and assume she didn't intend it that way, but is just saying so to pre-empt criticism of the upcoming film in which that fact is revealed? Or do you read it as somewhere in-between, that maybe she had some vague ideas at the time that Nagini would be something slightly more than a snake (maybe even something in the vein of Crookshanks - a crossbreed of an everyday animal with a magical creature), and then later on discovered this Indonesian myth and retrofitted it onto her earlier idea? We don't know, and we'll probably never know. So if you take 10 people and they all have 10 different ideas about what Rowling meant - who is correct here?
What about, moreover, when texts are directly contradictory? In Book 5, Professor McGonnagal revealed that she has been teaching at Hogwarts since the 1950s, and attended Hogwarts in the early 1940s. Pottormore entries stated that she and Professor Sprout were classmates in the 1940s, which would confirm that text. It was also stated in the books that Professor Dumbledore was a professor of Transfiguration before he replaced Armando Dippet as Headmaster of the school But then, in the most recent film, we see Professor McGonnagal present at Hogwarts in the present-day of the film in the late 1920s, nearly 10 years before she was even born according to the original seven books. Moreover, in this scene, it is revealed that Dumbledore teaches Defense Against the Dark Arts, not Transfiguration, and that this is his beloved teaching position. So now we have to ask: which is the correct reading? Are the books the correct reading or the film? Are we supposed to read the film's scene as non-canon? an unreliable narrator? Did Rowling originally intend for McGonnagal to start teaching in the 50s and then change her mind? But that problematizes things further, as it demonstrates that an author's intent isn't absolute, but rather malleable? So now we need to figure out which version of J.K. Rowling is the author-ity? The one who wrote The Order of the Phoenix, or the one who wrote The Crimes of Grindelwald?