Fans have created a timeline of the Harry Potter series from a single piece of information in Harry Potter and the Chamber of Secrets.
A short film with the movie series cast, The Queen's Handbag, was produced in 2006 as part of the 80th birthday celebrations for Queen Elizabeth II.
The skit violates the dating convention by having the characters reference the event, even though for them it should still be the mid-1990s.
For the sake of convenience, this dating system will be used by the Harry Potter Wiki for all Harry Potter articles.
There are numerous contradictions in the timeline, though it should be noted that, in the FAQ section of her website, Rowling has admitted having difficulty with managing mathematics, so perhaps perfect internal consistency is not to be expected.
Since the celebration was commemorating the five-hundredth anniversary of Nick's death, this seems to say the scene takes place on 31 October, 1992.
This timeline is reinforced in Harry Potter and the Deathly Hallows when the graves of James and Lily Potter confirm that they were born in 1960 and died on 31 October 1981, further reinforced in Pottermore when the Death Eater riot on the Quidditch World Cup is stated to have taken place in 1994, and further yet in Harry Potter and the Cursed Child, in which the Triwizard Tournament is mentioned to have taken place in the 1994-1995 school year.