V-n Diagrams

I have been playing around making V-n diagrams for the various airplanes
I rent from my flying club.
I made one for our P28T-201RT and was looking for the numbers on the
PA32-300.

The one item for the PA32-300 that would not follow the formula for
calculating the lift line was Va. The book shows it as 132 kias, but the
formula generates a speed of 103 kias for the intercept of the 3.8
load limit line.

Can anyone explain this discrepancy?

It is interesting to note that Piper does not allow any negative
maneuvers in the Normal catagory, on 3.8 positive. (Cessna does, -1.52.
Another reason to own a high-wing! ;-)))
Another interesting item was that both have a Vne of 192 kias and Vfe of
108 kias.