We have seen cases of abnormal values (> 100%). Regardless of the cause we can and should assert that CPU/disk/memory percentages 0 <= x <= 100%.
Related to #653
The values returned by WMI often add up to > 100% so I think if we added such an assertion we would drop points often. I believe this may have been caused by a bug in WMI or how these values are reported, but I'll have to see if I can find the source for that.
We haven't seen these cases since we bundle our own version of sysstat. Closing.