You don't need to know anything about the new stuff. You used to be able to get Sudafed; it worked. It was moved behind the counter for $REASONS. You've got enough to guess that the new stuff is some kind of inferior substitute and that you're only going to be able to get the real thing during pharmacy hours.
That was 20 years ago. Plenty of people never experienced the good Sudafed and have no idea it moved.