I forget the details, but I recall reading about Cook's voyage to the west coast of the US, specifically to the Nootka sound/Vancouver region. There was some evidence that he had advance knowledge of the region from Spanish exploration a few years earlier. My fuzzy memory says he had a copy of a journal from the Spanish captain. How he got it is something of a mystery, but if one likes a spy tale, one could conjure up espionage. Likewise, there were rumors that the Spanish had previously visited the Hawaiian Islands. And the dutch, and French had already visited Australia. If one follows the espionage tale, it could be construed that Cook was sent on a mission to discover, and claim, that which had already been discovered. Not to dismiss his well documented competence, but I think the world was a little more understood than when Columbus set sail. There were certainly a lot of gaps in knowledge, but I don't think he was so special that another captain who had gotten command couldn't have accomplished the journeys.