The Nyquist stability criterion is a basic result which can be applied to any transfer function.
Additional information is also available.
Thus, more information is available from the Nyquist plot than just the number of unstable closed-loop poles. This principle allows one to determine the difference between the number of zeros and the number of poles in a specified closed region of a complex plane. The complex plane that we are interested in is the s-plane. The items of interest to us are the closed-loop poles of the system. This is the region of instability.