I never even heard of this, darnit.
The varying amounts of refunds interested me, and I wanted to see what the settlement was all about, so I googled. And found:
"Payments were calculated based on several factors, including how much you paid, the quantity and quality of the diamonds you purchased, the amount of money that is available for your Class or Sub-class, and how many Class Members filed claims."
So that explains the varying refund amounts.