It depends on the location of the individual farm that grows the hops, weather, harvest time, year harvested, and so on. The information I saw mentioned that a late harvest in 2011 caused some US Saaz to have much higher AA% than expected. Since AA changes with all these variables, I would expect that the 8.1% listed on the package is likely to be accurate. It would probably be a good idea to update the AA of the hops in your brewing software to accomodate for this difference.
"Give a man a beer, and he will waste an hour. Teach a man to brew, and he will waste a lifetime!" Bill Owen