We do not know how it is possible to address failures by testing only X number out of so many houses. We cannot understand how an energy efficiency label can be assigned to a home that has never been inspected or tested, as some “energy-efficiency” programs do.
We have a word for this practice: F-R-A-U-D.
No, we do not sample homes as it is our experience that the number of failures precludes any possibility of sampling.