  The SWKB quantization condition is an exact quantization condition for the
conventional shape-invariant potentials. On the other hand, this condition
equation does not hold for other known solvable systems. The origin of the
(non-)exactness is understood in the context of the quantum Hamilton--Jacobi
formalism. First, we confirm the statement and show inexplicit properties
numerically for the case of the conditionally exactly solvable systems by
Junker and Roy. The SWKB condition breaks for this case, but the condition
equation is restored within a certain degree of accuracy. We propose a novel
approach to evaluate the residual by perturbation, intending to explore the
correction terms for the SWKB condition equation.
