There are frequent references to the
Spanish Flu outbreak, and several characters in the series contract it. However, the "Spanish Flu" epidemic took place in 1918-1919, while the events in The Nine Tailors took place in 1928 or 1929. The character "Deacon" spent 4+ years in prison before escaping, impersonating a soldier and being shipped to the Western Front in France (1918), then spent a further ten years incognito as a French farmer before returning to England in the major action of the story. This made the narrative time frame 1928 at minimum, and there was no Spanish Flu outbreak then.