Even F5 tornados don’t leave a predictable “swath of destruction”. There are widely variable patterns of damage inside an F5 tornado path ranging from F0 to F5. The worst damage corresponds to the paths of the individual microvortices or “suction spots” that make up the tornado, but even these vary in intensity. The damage criteria reference building materials and (to a much lesser extent) trees and foliage, so if there weren’t any buildings affected in a portion of the tornados path it is very difficult to ascertain the power of the tornado in that stretch. Initial estimates almost always overstate the power of the tornado. Uncertainty comes with the territory, I guess.
Apparently the Parkersburg,Ia tornado was an F%. I do not know if there were existing structures engineered to withstand an F5. Interesting note:All seven fatalities in that tornado were sucked out of the basement where they were taking shelter. Amazing power.