"The venous system in the brain is very forgiving," said Dr. Ellen Marder, a Dallas neurologist who recently published a study comparing the veins of MS patients to those without the disease. "There are a number of people who are missing veins or have them on only one side. These are people who don't have multiple sclerosis. There are people who lack certain large veins and they drain their blood just fine through other veins."
Dr. Marder makes a good point. It's a bit of cognitive dissonance to think of how important we consider the jugulars, then think of these situations where people are missing veins seemingly without consequence. HOWEVER it seems to me that the truth is that the venous system is forgiving...up to a point. I did not have just one jugular nearly entirely blocked, I had two jugulars that way. That I got this far into life is a sign that the venous system is flexible and forgiving. I did not drop dead at birth! But there is a distance between dropping dead at birth and living a full healthy life.
To me the number of MS patients with multiple blockages, such as both jugulars blocked, or a jugular and an azygous, fits with what Dr. Marder is saying. The venous system is forgiving, it can compensate perhaps for one blockage. But it starts to fail when it is asked to compensate for more blockages. Add some genetic susceptibility for immune system over-reaction and it gets even worse.