Please correct me if I am understanding you wrong.
At 3 years it wasn’t that the medicated kids had regressed, it was that the non medicated kids had become better at coping and regulating themselves.
Is that what you meant?
Based on my personal experience..yes. You learn to cope.
Coping is a big part of dealing with ADD/ADHD. I can say this first hand. I learned skills that I needed to learn.