An acknowledgment shows that someone saw the change, but it does not tell you whether they understood what is different or why. Understanding usually shows up in two ways, through a short check about the change itself and through how the person actually performs the changed step afterward.
A few targeted questions about the specific change are more useful than a long quiz on the whole procedure, and execution records show whether the new step is being done correctly in the field. Together those give a much better picture than a list of signatures, especially for changes to critical steps.