I'd request more x rays and /or MRI of neck and get that extra vertebra or rib clarified...
Might be wise to look for a TOS experienced surgeon first..or afterwards if extra ribs do show up..

The car accident could have made for some internal scar tissue , also a prior whiplash can be a factor with TOS and ageing..

Explore all of our sticky threads , so much saved info , knowledge will helps you know if a DR or therapists is helping/helpful or not..
Bad PT / treatments can make it worse...

Any symptoms with your neck?
tight painful, any general soreness or limitations in range of motion?
trigger points, muscle spasms?
Sometimes you don't notice those until you get a massage, PT or DC and then you might notice how much looser the neck & upper back can feel..

But if something is compromised and pressing on the nerves for the arms then you may not have the neck & upper back issues as much..

Did you find the blood flow test to check if blood flow is cut off when arms area raised (turns hands/arms white) then blood rushes back when hand are lowered turning then reddish/pink.. small % of normal population has this without issues..
It would indicate some blood flow issues also if your hands turn white..
If not then possible nerve or NTOS.
VTOS is Vascular issues..
one from the sticky - Nismat / Patients / Injury Evaluation & Treatment / Head Neck & Back / Thoracic Outlet Syndrome: More than just a pain in the neck