Giving an easy example:
Ship Group A: (Options F, G, H)
Ship Group B: (Options L, M, N)
Ship Group C: (Options K, Y, Z)
If the player has F, G, and H in their port, Ship Group A cannot be rolled in the first place.
If the player also have L, M, and N in their port, Ship Group B cannot be rolled in the first place, either.
If the player strikes Ship Group C, and only has K and Z in their port, they will receive Y because no other option exists.
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If the player has F, G, H, L, M, N, K, Y, and Z, Ship Groups are replaced by [Compensation] which will be triggered whenever the Ship Group area is rolled (or triggered from bad luck prevention).