I have studied the numbers available from various desk studies,

The point about this report is that it isn't based on desk studies, but on sampling. That's a fallible method, too. It's going to be a long time, if ever, before accurate figures can be estalished.

The people in charge of the invasion and occupation have made it very clear that they are not interested in gathering those kind of statistics (though I believe they had a legal duty to do so), and that has made it far harder than it should be for accurate figures to be determined.