I have an older family member who is severely mentally disabled and always has been. His medical records diagnosed him as r*tarded. The adults diagnosing him at the time didn't understand enough about mental conditions and their differences when he was a child. So kids like him were diagnosed with that. It did have more 'legitimate' uses than it does in our current context. Doesn't make it good or right, doesn't mean they shouldn't have tried to be more specific either. That legacy leads to now where we have the nuance and resources to do better. I am glad it's more and more relagated to the past as it's consistently been used to dehumanize people.