I've created a head rig and animations using morph targets. In between frames, the values of each morpher targets are sometimes exceeding 0 and 100 (so either going -678 for example having been set to 0 in a frame before, or going to 3229 having been set to 100 a few frames before). This hasn't caused to many issues in Max…
Do you intend on using the overshot morphs? If so then there is no easy fix. But if you are just looking for a way to cap the values of your curves that's easy with a limit controller.