TIL the Treaty of Versailles ending World War I also included a clause establishing concert pitch as A = 435 Hz
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Concert pitch - Wikipedia
https://en.wikipedia.org/wiki/Concert_pitch#19th-_and_20th-century_standards
[T]he multilateral treaties, conventions and agreements of an economic or technical character enumerated below … shall alone be applied as between Germany and those of the Allied and Associated Powers party thereto:
. . . .
(22) Convention of November 16 and 19, 1885, regarding the establishment of a concert pitch.