Credit: Manuel Harlan

Not even J.K. Rowling can remember every aspect of Harry Potter arcana, it seems. As usual, Sep. 1 marks Hogwarts Day, the date that the Hogwarts Express pulls out from Platform 9 and 3/4 to take a train full of eager students to the world’s greatest school of witchcraft and wizardry. To commemorate the holiday, Rowling tweeted congratulations to Harry Potter’s son Albus Severus for his first day of school at Hogwarts. The only problem is, she got her dates mixed up — or at least, fans thought she did. Rowling deleted the original tweet and issued an apology before returning to pen tweets about U.K. Labour leader Jeremy Corbyn.

Some fans still weren’t convinced, however. In Harry Potter lore, the climactic Battle of Hogwarts took place in 1998, and the new play Harry Potter and the Cursed Child (which begins with Albus starting his years at Hogwarts) is set 19 years later. Some people think that means 2016; some think it means 2017. The world may never know.