I couldn't find a definitive list posted, so I did some deduction.
As you are already aware from your map, Groundspeak (and therefore project-gc) counts autonomous regions as countries as well. You already have some, like Isle of Man, Aland, Gibraltar, and Faroe Islands.
Looks like you're missing Greenland, the two Channel Islands (Jersey and Guernsey), Russia, Turkey, and Belarus. I went to project-gc profiles to verify that these six all count as "countries" on the project-gc map of Europe.
edit: OK, those are likely the six you came up with. I'll snoop around some more to see if I can come up with the other two.
You're also missing Svalbard and Jan Mayen and San Marino. You can see all 53 listed on KateBum's profile.