I read one source from a doctor that the changes were FDA mandated, but I cannot find any proof of this or what changes were supposedly mandated.
Personally I don't like any hormone replacement therapy. All they do is make the glands lazy and shut them down. Therefore, in my opinion natural or synthetic thyroid hormones should not be used except in cases where the thyroid has been damaged beyond function or has been removed. Otherwise, the base of the problem, which is usually nutrient deficiencies should be addressed instead.