From a publication standpoint, this is the earliest story in the series.
The black-and-white square earrings worn by Kari Matchett (Carla Lovchen) were also worn by Francie Swift as Margot Dickey in Nero Wolfe: Christmas Party (1.09).
The Nero Wolfe story on which this episode is based was published in September, 1939, just prior to the outbreak of World War II. This explains the involvement of British and German spies, the political situation in Yugoslavia, and Wolfe's statements about the combatants to whom he donated money.