What are rumours?

Rumours show what special islands are revealed in that area. The game only shows up to 3 of these rumours, randomized out of the possible fixed options for that area. By moving anything in your inventory, or activating a Saga, the shown rumours list is re-generated in game, by repeating this process you can get a good feeling about how many special islands there are before revealing it with a logbook. Use the Logbook planner to optimize your grand expedition gameplay.

Throughout example: an area might have 5 special islands, when you hover the area it'll show the rumours corresponding to 3 of these. E.g. island 1, 3 and 5. Refresh the map by moving something in your inventory, now the rumours might show 5,1,2. Refresh again, 4,2,5. By tracking all the unique occurrences we can surmise that there will be at least 5 special islands.

If there are less than 3 rumours, then there's no reason to refresh the list. We know for a fact that is the amount of special island types.

A single rumour can also mean there's multiple of the same island in the area, e.g. if Cold as ice rumour shows, the reveal might spawn 3 Frigid Bluffs grand expeditions, meaning a confirmed GE count is a minimum.