Cannot add drawing substitutions

When I try to create drawing substitutions, each time I add a new version of, for example the chapter’s mouth on a new frame or keyframe, it changes every drawing representation of the mouth on all of my frames or keyframes. Is there a preference setting or tool that I am missing somewhere? What am I doing wrong?

If you copy and paste from the timeline you will actually be using the existent drawing. You have to create a new drawing from the timeline, or you have to paste some thing in the drawing window in an empty frame.

Make sure you click the ‘new drawing’ button on the timeline view toolbar before drawing a new substitution. If you cannot see the toolbar, you can find it under Windows>Toolbars>Timeline View

or you can right-click and click insert keyframe and duplicate drawing