Well, of course, they've all shortened their given names. Van was Ivan, Yul was Yuliy, Angel was Angela, Cher was Cherilyn, and Anton was Anthony. I'm sure they no doubt all had good reasons for the slight changes. They probably all thought they either sounded better, or it suited their characters more.
Most people have nicknames of some sort during their lives. My own three children have always been known by names that they weren't given, although I don't think they had nicknames at school; as nor did I.
Some of my friends at school were called Smiley, Monty, Sparks, and Po. Po has continued with the name throughout his life, and is still famously known as Po today.
When we selected names for our children, one of the criteria was that they couldn't be shortened or changed into something 'rude'. We also needed names that we could SHOUT (not unlike a dog's name).
Choosing names is important, but shouldn't be fretted over; nor should they be overly-crazy in some desperate search for originality. One can only feel sorry for 'The person previously known as Prince', or X Æ A-Xii, or even Toadie.
We have friends named after M1 Service Stations, and after the seasons, but it's probably far better to choose a name that one could use either as a road-sweeper or a brain surgeon. A certain amount of social equality/mobility would probably be wise.
What it comes down to is having a name that one can go through life with, without having to cringe every time you repeat it, or, even worse, having people laugh.
So, To Wowie Bowie, who changed his name to Duncan Jones, I say "Well done".