The article referenced mentions of goitre in Switzerland from Victor Hugo in 1839, Mark Twain in 1880, a medical survey in 1883, and Roman authors like Vitrivius and Pliny the Elder. It also mentioned that the iodine idea had been going around for a hundred years before the activities of the heroes of our story.

Iodine had not been seen as a successful cure before because excess iodine causes a horrible condition. The key difference here was that Hunziker proposed regular use in minute quantities, and then Bayard tested the hypothesis with careful measurements and convincing evidence.

Swiss geology (retreat of the glaciers 10000 years ago) meant that the normal local products that would give a population iodine (milk and eggs) were themselves iodine-poor. A few parts of Switzerland which were not glaciated (i.e. Jura) did not have iodine deficient populations.

Other places in the world had different geology and this different levels of natural iodine.

Goethe wrote in 1779 about his travels to Switzerland: “Die scheußlichen Kröpfe haben mich ganz und gar üblen Humors gemacht (“The horrible goiters have given me a very bad sense of humour”). Definitely plenty of earlier historic evidence.