Are you receiving a message in the bottom right of the map that you have locations that are unknown? If so you can add those missing countries by choosing "edit locations".
If not, it's probably a matter a space. You can change it by right clicking on the country and change the mark label to "always show" instead of "automatic". You can then adjust the box or the font to make them fit.
If that doesn't work you may need to add these manually: right click on the country --> annotate --> mark, point, or area. After you've added them, again, you will need to format the box/font.