The new Wizard of the Month has just been posted on jkrowling.com:
Hey, wait a minute... Dumbledore died in 1997! That's a fact, albeit one that is not stated explicitly in the text. But it's easy enough to figure out. We know from the text that Harry Potter and the Chamber of Secrets took place during the 1992-93 academic year. (How do we know? Because Nearly Headless Nick celebrated his 500th Deathday in that book, and the cake said he died on October 31, 1492. Say, Google Calculator, what's 1492 plus 500?
Thanks, Google Calculator. So we know that Harry started his second year at Hogwarts in September 1992, and went home for the summer in June 1993. Knowing that, we can determine that Harry Potter and the Half-Blood Prince, the sixth book, takes place during the 1996-97 academic year. And since Dumbledore was killed shortly before the end of that school year, he must have died in 1997. Not 1996, you silly old leg-before-wicket Scottish person!