According to this timeline, Amelia would be seventy years old in the eighteenth book, "Tomb of the Golden Bird", set in 1922–23. In "The Hippopotamus Pool", however, the Introduction contains what is supposed to be an excerpt from ""The National Autobiographical Dictionary" (45th edition)", in which Amelia herself states that she was her late twenties at the time of her first visit to Egypt. The statement is footnoted, and the footnote provides specific instructions not to question the discrepancy (pp. xii and xvi.).