Even in case of my wife her left carotid artery is 100 % blocked. It was detected when she had a stroke on the right side of the brain. Doe to advanced age of 70 years they do not want to take risk to open the blocked artery.
Ask your doctors why they didn't tell you about the circle of willis, it supplies blood to the brain and is fed by 2 vetebral and 2 carotid arteries. You don't need all 4 to keep the brain supplied with blood. One of mine is 100% blocked. Blocking those arteries does not directly cause a stroke, usually it is because the artery tears, clots, and the clot lets go travelling to the brain. Ask for a basic brain anatomy lesson from your doctor. Their answer will tell you if you should find a new one or not.