Wouldn't the data they gather include artifacts of improper usage and ultimately feed into their conclusion on whether mandates work?
If you look at the series the different in case rates started before the mandate, making me think it's more about behavior differences in cities vs rural areas than the mandate (makes sense).
I'm replying to the point that mask mandates do not imply proper mask usage, which is almost certainly correct. However the usage errors the general population will make with masks should show up in the overall case rates and be accounted for in the data and conclusions here.