1) . . . my ancient history teacher sucked, then. Still, though - knowing the world was round doesn't mean you'd know its exact geography.

2) Point. Still and again - doesn't mean they know about this mysterious land around the world.

4) . . . I . . . have never heard this, but I guess that doesn't mean anything, does it? (The way I've always had it is that Merlin could see the future, but that didn't mean he knew everything.)