Logically it’s correct not to include all. Since you want to sort them by like/unlike counts, they must have received votes first. It doesn’t make sense to include those which don’t have any counts.
You can try by hitting the “Update Like Meta” button on the plugin admin settings page. It assigns/updates like meta data for those who do not have this entry. If this doesn’t work for you, can you please share the code you are trying with?