Did they check the C spine MRIs X Rays very closely to verify that there are no extra cervical ribs?
Sometimes they are missed, or as children grow , so do the extra c ribs and they begin to cause more problems..

If it has been awhile since the imaging, a re check or at least fresh x rays might be a good thing..

c rib images-
https://www.google.com/search?q=cerv...IVVP5jCh3FgAi2

Our Thoracic outlet syndrome (TOS) forum has more related info or use search tool for past posts.
http://neurotalk.psychcentral.com/forum24.html

Expert PT or expert chiro eval/assessment might be helpful .
Often MDs will not even touch or palpate anymore for issues... they leave that to the PT persons..
Any PT for the neck at all yet?