Flutter-- Normally one would like to have all the operating regime below the onset of flutter, analogous to the design of engine crankshafts in regard to torsional vibrations.
A moot point maybe, but possibly a bad analogy
in this context - engine crankshafts usually run through their torsional vibration speeds, sometimes work near their 2nd harmonic (I think!). Torsional dampers (metalastic bushed pulley wheels etc) control their worst effects on NVH and crank fatigue life.
The crank is simply made strong and stiff enough to have a sufficient fatigue life - one 4-cyl in-line engine I knew well had an easily recognised resonance at 5500 rpm, smoothing beautifully above that. Overdrives would in the early days help one avoid sitting at that rpm, their use often being ascribed solely to reducing fuel conusmption
Whereas as you say, flutter speds have to be a known margin above placarded safety speeds.
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Thanks for your analysis OE... it might be worth reflecting that the VS could well have been the one major component that had no counter-balancing drag (hydraulic) to it's forward inertial forces under this hypothesis - sticking up high as it does?