Originally posted by Slynx Jewel:

i think he was talking more about mistland then new dungeons in the mountains.
but yes. the game generates new things as you explore. so it's likely that you'll get updated mistlands (and mountain dungeons) only in unexplored parts or new world.

all spawns dung boss locations and traders will be in the same place for every seed with the same name there is no random gen beyond the seed name

you can use a map genarator where you put the seen name in and it will show you every detail of you're map where the boss locations are and the 3 possible locations the trade can spawn it will also show you where every iron mine troll cave and skelly den is located because they are not random.