Source: https://en.wikipedia.org/wiki/List_of_highest-grossing_films#High-grossing_films_by_year
"Because of incomplete data it cannot be known for sure how much money some films have made and when they made it, but generally the chart chronicles the films from each year that went on to earn the most. In the cases where estimates conflict both films are recorded, and in cases where a film has moved into first place because of being re-released the previous record-holder is also retained."