As I understand it, there is a wide range of acceptable spoke tension on most traditional style wheels.
Park Tools will likely aim their guage at the lighter end of acceptable tension to save themselves from the trouble of people trying to claim against them if they damage components while going by their guage.
so if I were you, I wouldn't sweat it too much. I certainly wouldn't back off tension on any wheels that already have some miles in them. Maybe you could use the guage and build to less tension on your next set, if you are comfortable with that.
i think it's more important that your tensions are even around the wheel. (same side obviously). How do they fare on that score?
Roger Mussons wheelpro book has an interesting take on tensiometers.