Once your seed is loaded into the tracker, each location will start with a zero indicating you have not obtained any Important Checks from any of the locations.
Any worlds that indicated as complete (with default settings, completion is indicated using a blue number) means there are no Important Checks there.
In the screenshot above, we know Disney Castle has no Important Checks (though there still may be useful items/tools there).
As you find Important Checks in the game, the numbers for each location will track the number of Important Checks found there. Once the tracker indicates a world is complete, all Important Checks there have been found.
In the screenshot above, 3 Important Checks were found in Olympus Coliseum and the world is now indicated complete, meaning no more Important Checks are located there (though there still may be useful items/tools there). Additionally, 3 Important Checks were found in Beast’s Castle, and since the world is not indicated complete, Beast’s Castle must contain at least one more Important Check.