Are the raw test scores actually fitted on a curve beyond the mean and sd normalization?
Yes, they are.
First they are transformed to a percentile rank, then transformed to a position on the bell curve (with mean 100 and sigma 15) having the same percentile rank.
Why is this so, I have written in another comment. The reason is backwards compatibility with an older formula, which used a different approach (which does not scale beyond childhood), and got similar values “naturally”.
Yes, they are.
First they are transformed to a percentile rank, then transformed to a position on the bell curve (with mean 100 and sigma 15) having the same percentile rank.
Why is this so, I have written in another comment. The reason is backwards compatibility with an older formula, which used a different approach (which does not scale beyond childhood), and got similar values “naturally”.