My understanding is that in general there no need for supplements with a normal, balanced diet, especially with eggs, dairy products, grains, and others if iodine is naturally present in the environment.
So if Switzerland imports a lot of those, raw, or in prepared/processed food, or even the animal feed for its hens and cows the Swiss today probably already get much more iodine in their diet than 100 years ago.
I was curious about your point about normal diet and have just looked it up. According to tables 1 and 2 in this article [0], it may be hard for some people to get enough (RDA) iodine from normal, not fortified foods.
But the point is that Switzerland's environment is especially poor in iodine hence the specific health problems it used to have, and which were much less serious in neighbouring countries.
