The Godfather

Continuity: The age of Tom Hagen when he moved in with the Corleones is never consistent. At the start of Book I, Michael says Tom was 12 when Sonny brought him home and demanded they take him in; later in Book I, Tom says both he and Sonny were both 11. Then, in Book III, when recounting how Sonny had taken part in an armed robbery when he was 16, Don Corleone says that Tom had been living with them for three years at this point, which would place Sonny and Tom at 13 when Tom moved in.

Continuity: The war between the families is referred to as the Five Families War of 1946 at the end of book I. Later on it's suddenly the Five Families War of 1947, even though it begun with Michael killing Sollozzo and McCluskey in early 1946.

Continuity: In book I when Michael leaves to see his father at the hospital, the narrative text states that Kay Adams would not see him again until three years had passed. When they are reunited in book VII it is often stated that they've been apart for two years, not three.