If an adolescent truly had insufficient iodine in diet for 2.5 years, a goiter would have resulted, right? or would there have been other symptoms?

Depends: The goiter would be a late stage development in this process as the gland increases in size to try making hormone that requires it.Chronic fatigue, increased hot/cold sensitivity,slowed growth, weight gain would likely precede it.It is hard to avoid iodine in the USA where it is added to salt purchased in stores or in processed foods. Blood iodine levels can be checked if deficiency is suspected.