Other than those in adventure 1 (which is in the box set), all locations introduced inside an adventure are not reused later in the adventure path. This is because of a paradigm we call "the Afghanistan principle."

At Lone Shark, we're big fans of sending games overseas to our troops. But given where they're deployed, our troops often don't have a friendly local game store wherever they are stationed. So I would not be surprised to discover that one of our fans in Afghanistan had a base set and adventure 4, but not adventure 2 or 3. So asking her to use a card from adventure 3 when the closest copy of that card is several countries away would be unfair. So we don't do it.

The Afghanistan principle guides decisions like "all role cards are in the base set, even though they're not gained until adventure 3" and "if a henchman appears in two adventures, he shows up in the base set."

These are things we think about when designing games. Hope that helps.