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Question about The Starfarers of Catan 5- and 6-Player Extension - Should the colored number chips of the 5-6 player extension be mixed with the number chips of the base game?

Answer

They should be mixed. Since the chips are marked on the front side, you can mix them, distribute them face down, and separate them again after the game is finished. If the cards weren’t supposed to be mixed, different card backs would have been used to distinguish the cards.