"Planet Nine is an undiscovered planet in our solar system" cal. 200, i.e. depends on context/application.
Evidently there was a Planet Nine, but it is long gone, hence the "it depends" calibration result. Is the context now or anciently? We're simply seeing the ripple effects of its former presence in the solar system.
From Wikipedia, cal. 450:
Many of the objects were also ejected from the Solar System after encountering the other giant planets. The large unobserved populations and the loss of many objects led Shankman et al. to estimate that the mass of the original population was tens of Earth masses, requiring that a much larger mass had been ejected during the early Solar System. Shankman et al. concluded that the existence of Planet Nine is unlikely and that the currently observed alignment of the existing ETNOs is a temporary phenomenon that will disappear as more objects are detected.