I don't know what you mean by narrative control over the world. So I'm saying if it's established in the fiction absolutely none of the ships are familiar to the sailor in the port at which the party finds themselves, then it would be dysfunctional play on the part of the player of the sailor to disregard that fiction and say anyways they try to secure free passage on the Comox which they know is in port because they served with members of her crew.
Narrative control means that the player controls the narrative; the player makes design decisions about the world outside of their character. In the case of the sailor, there is no way I can list everywhere they have not been or do not have contacts, that's a nearly infinite list which would include things I hadn't even thought of ahead of time. As a DM if I know they are sailors from the Seer Sea, I have a general idea of what trade routes they were on and where they may have contacts.
My players and I discuss their background, and they are free to add to that background. I just want editorial control which means big changes are done offline, not during gameplay. As always everyone is free to ask about details of their current situation, things they may or may not know. In my example of someone from the Seer Sea, there is a very slight possibility they'd know someone halfway across the world in which case I'll have them roll a percentile die. When in doubt, roll for it. But the player can't just declare that while they're in Jotunheim that they happen to know someone who sails the Sea of Fire. Before you protest that no one would do that, I've absolutely encountered people over the years who would.