Here is an example of such a campaign
https://tools.wmflabs.org/isa/campaigns/39
In the result area, there are
410 contributions of "unknown" country
Then
328 contributions from "Ghana" and so on
But... it is not logical that so many records are tagged unknown country when the biggest majority of images are related to a country. I believe it indicates "unknown" when the person does not choose to work on a specific country. But the country associated by the image is known.
So the information displayed here is not the proper information. That should not be "the "unknown country" selected by the player, but it should be the "country the image is from".
Ultimately, there should normally be VERY VERY VERY few "unknown country". Only those images that are REALLY tagged with "no country" at all.
If a player has not selected a country, but the image he improved is from Ghana, then it should be added to the "Ghana" country, not to the unknown country.