Equally, who would have recognized a flat spin anyway - would the instruments tell you? How would today's AHRS electronic instrument sensors translate the forces of a spin? It used to be that the only dependable clues were the slip indicator and the rate of turn indicator (turn & bank) and airspeed...
Apart from instrument indications, due to loads, the crew on the flight deck would have been thrown violently forward and to the left or right, depending on direction of the flat spin. Perhaps unable to move at all for periods of time if the rate of spin was high enough.