I think that once a bottle is open, the location, known the to player with the bottle, should also become discoverable by everyone after “x” time. You, as bottle owner, would have a certain amount of time to get to the wreck. After that, anyone sailing by the location could spot the wreck on their own - it would not be visible on the map.
I think that would make wreck finding a bit more interesting and then everyone gets the possibility of hitting a random wreck to loot.