I wrote the Vne Auto chart for the S-76! It is a fine story in itself, and I think it illustrates the randomness of Vne determination.
The FAA requires that you must have Longitudinal Static Stability (LSS), where the stick position for any speed must be ahead of a lesser speed. This makes sense to any pilot, but the way it is tested makes little sense. The Normal pilot trims to a speed and notes the stick position, then flies to a new speed and sees that the stick position is a bit forward of the previous point and he is happy. The FAA (and their European friends) however do it by settling to a speed, and then advancing 20 knots without increasing power or collective pitch. They then check the stick position at the new faster speed (and fail to note that the new speed has created a 1500 fpm descent) and find that it is at the same place or even (heaven forbid) a little behind the slower point. They then declare that the aircraft has the dreaded negative static stability and must be banished. The fact that the screaming descent creates a large horizontal tail angle that pushes the nose down and forces the stick back completely escapes their sharp eyes.
Now back to the S-76. In the cookbook LSS test in a autorotation, you must trim to .9 times Autorotation Vne and then push to 1.1 times autorotation Vne and if the stick comes back, you have a problem. I was the guy who found out that 1) the FAA has no rules on what the auto Vne must be and 2) at 136 knots or slower, the LSS stick check worked well. As a result, a fine Sikorsky engineer (Dick McCucheon) and I wrote that Auto Vne chart on a piece of paper and it became the new placard. John Dixson was in the back with a cup of coffee, laughing too hard to help, as I recall.