Many certified manufacturers have similar limits where you can use IAS up to a specific altitude. Above that you revert to TAS. VNE is a combination of flutter margin and structural strength. Flutter margin is generally a true airspeed function. Structural issues are IAS related. Itís quite common to have a aircraft where structural failure will occur before flutter. In that case IAS is the appropriate measure for VNE. From everything posted here it sure appears that Vans is comfortable with flutter limits up to 16,000 PA and 136 knots indicated.