I wonder if they were referencing the same study as the Celiac Disease Center is for their 60% number:
Unfortunately, the celiac center doesn't reference the research specifically, either. But the research center makes more mention of the fact that diet compliance can affect the results.
The study results seem to vary, otherwise. I wonder if they are more consistent when you look at them by area, perhaps? Some differences in brands or gluten free food laws that might affect the patients' food? Or maybe better patient education and support?
I know the study Kareng mentions is from the Netherlands, but a study in Italy and in the USA had different results. It seems weird that the results would be so different without something else going on that is maybe not being taken into account by the researchers, you know? :-/