Capitan Smith was 20 miles, If I remember right, off the usual course would he have informed anyone on shore of that? It's a big ocean.
Certainly it is, and I mentioned that. Still, searchers aren't going to the one point on the globe they think the Titanic should be at, not find her and just go home. They're going to look around. As whatever search pattern they run expands, it seems probable that, even if they're 20 miles off (which isn't much on an Atlantic scale) to start, some debris would be found. Maybe not much, but finding any would tell them that something cataclysmic had happened.