Trog, thanks for the thoughts. The issue is not specific to the RJ.
The background thinking is to explore accident situations, where an aircraft can be shown to meet aerodynamic / control certification requirements - static conditions, but in dynamic accident situations the aircraft is unable to achieve the level of control which might be assumed from certification.
Re the Cn parameters, the issue might be best related to Cn dynamic, but probably not as a classic theoretical problem.
As another example, hopefully, not to confuse the situation further, consider rudder ‘crossover speed’ - a static wings-level test point. By definition this could not be achieved (control limit, constant speed) if the aircraft was already rolling because greater control power is required to first stop the roll, and second return the aircraft to wings level. The limiting roll power is encountered earlier in dynamic ‘failure’ conditions than at the static certification test point.
This issue represents a gap between certification requirements, and the practical control limits encountered in rare accident situations, which could be misinterpreted by investigators.