I actually only found one case of a girl who had been diagnosed with AS and was found to have severe vitamin d deficiency. It was in several different websites, but the same case each time.
Would you kindly post links to the cases you found? I would love to look into this more.
They now understand how vitamin d works on the immune system better and I believe it acts on IL-17 and IL-23, both of which have been found to be integral in AS and related diseases. Something to do with how the B cells work and inhibiting T cells.
That said, if you're that low on vitamin D, I hope you are on prescription strength to jump start it. I was found severely deficient several years ago. After six months on prescription strength, my levels were back to normal. However, I now take between 4,000 and 7,000IU a week to keep my levels up. Having been severely deficient, you will also have to take high doses for the rest of your life. I vary it depending on how much sun I'm getting.
I'm glad you've come back. Stick around.

Warm hugs,