Well, it was an amazing link but not what I was looking for specifically. I think it may be the size (thickness) of the needle for working with specific fabrics. I did find a link for Boye needles that discusses using a number 2 for lighter fabrics and a 5 for heavier. Does that sound right?
In the meanwhile I had a happy discovery! The #13 vs for my Alvah also fits into my VSIIB White! This White is so weird. It sews with the handwheel turning towards you and the shuttle that came with it was made for the White hollow bobbins, of which I have 1. It won't sew with that shuttle but when I started comparing it to the shuttles I already own imagine my surprise when the Alvah's look identical except for the point on the inside of the White shuttle.
On a whim, I took the shuttle out of Alvah, complete with threaded bobbin, and tried it on the White. Success!!! Perfectly even little stitches!! Happy day for me!! Hopefully this is an ok thing to do.