Assessing the accuracy of the PER measurement is not trivial. It is itself PER dependent and increases disproportionately with PER value. For a typical PER of 25 dB, the PER measurement accuracy can be given to be ± 0.5 dB.
PER Measurements with values above 35 dB have a much larger measurement inaccuracy in the order of already a few dB and should not be taken too literally.