I'm not sure about the American editions (by Mayfair IIRC?), but for the German editions by Kosmos the answer is yes. The base game as well as the expansions had the material for 3 and 4 players, and all expansions and the base game each had an individual extension for 5th and 6th player.
The expansions and their 5/6-extensions only contain the additional ...
You cannot add in multiple exit points on a single hexagonal shape.
You can exit from a single point of entry or
You can continue a hexagonal shape after completing one full circle in both directions to extend the road further.
There are many rules in Catan, and this one can be debated but we have played this way several times.