As a native English speaker, I was mystified by the question as well. I actually happen to have an Rx bottle right here. It says:
"IMPORTANT: Finish All Of This Medication Unless Otherwise Directed By Prescriber."

I can remember in high school taking a "standardized" test that had several questions which involved interpreting a train schedule. We lived over 500 miles from the nearest train station and no one in the entire school had ever seen one before. 25 years later and I still haven't had to read a train schedule!