It is implied throughout the series that Hagrid was given that position within a few years of his expulsion from school in 1942.
But in one scene of Harry Potter and the Goblet of Fire, Molly Weasley reminisces about Ogg, Hagrid's predecessor; since Hagrid's years as gamekeeper appear to overlap with Molly's years at school, it seems unlikely that she remembers a previous gamekeeper.
Another mistake occurs in dealing with the attendance of Bellatrix Lestrange and Severus Snape at Hogwarts.
One such example occurs in Harry Potter and the Prisoner of Azkaban when Sybill Trelawney refers to 16 October as Friday, although 16 October 1993 was a Saturday.
This is usually explained as artistic licence on the author's part.
Or, Harry might have confused the Play Station with a similar console.
As most wizards are ignorant of how Muggle technology functions, the latter theory seems plausible, although Muggle-raised wizards knew much more about Muggles than the average wizard.
Despite its problems, this timeline is extensively used by fans and Warner Bros.'s timeline of the series (featured on the DVDs for Harry Potter and the Chamber of Secrets and Harry Potter and the Prisoner of Azkaban) contains dates that were interpolated from this dating system (such as Harry's birthday being on 31 July 1980 and his first defeat of Lord Voldemort being on 31 October 1981.) However, several anachronisms have crept through in the movies, such as featuring the destruction of the Millennium Bridge in the film version of Harry Potter and the Half-Blood Prince, even though the novel (and the film) are supposed to take place two years before the bridge was built.
In Harry Potter and the Order of the Phoenix, the Dursleys are seen to have a flat-screen television, which were not commonly available in the mid-1990s.In addition the Dursley's car, shown in the same film, bears a 2006 year registration plate.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.Often when dates are given, they are given with a day of the week that does not match with that date as it in actual history.There are also contradictions within the books in this area.