1.) You cannot descale a show without a sufficient error spike, no matter how low the absolute error is or how few artifacts there are. Example: The Eminence in Shadow has low error because it is very blurry, but it cannot be descaled.
2.) Error masks should not be used except for scenefiltering. They cannot and will not bail you out of situations where you are rescaling a scene with an incorrect kernel.
3.) Sometimes shows have multiple kernels. You cannot handle multi-kernel shows by testing the errors of individual frames and picking whichever kernel has the lowest error for each frame; this can and will result in scenes where frames are randomly and rapidly alternating between kernels. The decision of which kernel to pick must be done on a scene basis.
4.) Kernels must be analyzed by looking at the descale itself, not a same-kernel rescale (e.g. descaled with bilinear and then upscaled with bilinear). There are plenty of examples where a same-kernel rescale w