Iodized salt became available in 1924. When I see some old photos I sometimes see sparse eyebrows [I have been searching last few days]. Really noticed that with the 2 hour program about Thomas Edison for is early photos. He was born in Ohio and grew up in Port Huron Michigan, heart of the goiter belt. Some pix of his wife show very sparse eyebrows and she had many years of illness and was fat. Hard to work with photo portraits of women because of eyebrow pencils and the men always had high collars and neck ties so you could not see the throat.
Later when he moved to NJ, I assume that he would have been eating fish and the soils would have more iodine. And later when he spent a lot of time in Florida he would have been getting decent amounts of iodine.