Miss Kathy tells Chips that the ballroom in Vienna is where Metternich drew up "the treaty of the five kings" (referring to the Congress of Vienna in 1814 ending the Napoleonic Wars) "nearly 100 years ago." But the montage after Kathy's death makes clear she died before the Boer War (1899) and Queen Victoria's funeral (1901). 100 years after the Congress of Vienna was 1914, the start of World War I when Chips becomes acting headmaster and Kathy is spoken of as having died long ago.
After his retirement dinner, Chips is told of the assassination of "some Austrian arch-duke," leading to the outbreak of "the great war." Arch-duke Franz Ferdinand was killed on June 28, 1914, when public schools like Brookfield would not have been in session and students and faculty would not be on campus.