Maybe it helps if I sum it up:
A.&A.E.E. tested Spitfire K9788 (a Spitfire I) and it showed increasing long period oscillations, which means it is dynamically unstable.
NACA did not bother to investigate these, as "the well know long period oscillations have no correlation with the handling qualities of an airplane". NACA tested a Spitfire V. It evaluated short period oscillations, which all were damped satisfactory, and evaluated static stability, which was found to be neutral to positive flaps up, and negative flaps down.
Now I absolutely agree with NACA, in particular with the statement that the long period oscillations are irrelevant in terms of handling and in fact, dynamic instability was not atypical for fighter aircraft of the time. The Hurricane for instance, having gone through similar trials, proved to be far more dynamically unstable.
I've neglected the flaps down instability, which I consider irrelevant in air combat, because flaps down was no condition for combat.
As for the other qualities evaluated by NACA, be it good or bad, it sums up that there's nothing critical. Only characteristic, in that some points are rather weak, some excellent.
And all the hype about dangerously low elevator forces and changes to pilot notes - it was decided to add the part of the Mk II notes, which is repeatedly quoted here, after a total of 3 (three) Spitfire I's were lost due to mid air wing failures and investigation found that inexperienced pilots coming in fresh from training mostly in bi-planes needed an extra warning because they simple were not familiar with high speed pull outs and trimming in high speed dives.
The weakest point in terms of control were the fabric covered ailerons, whereas the overall control characteristics made the Spitfire an easy plane to fly, and an easy plane to fly to the limits. For a WW2 fighter aircraft.
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