You're forgetting several pretty big ones: China, Vietnam, Laos.

Did you mean to exclude China intentionally, or what was the main purpose of the question?

For Cuba from a search:

https://www.reddit.com/r/AskHistorians/comments/2l4xsq/why_did_cuba_manage_to_survive_as_a_communist/ https://www.reddit.com/r/AskHistorians/comments/1lypga/what_was_going_on_in_cuba_when_the_soviet_union/ https://www.reddit.com/r/AskHistorians/comments/2v8lxe/how_hard_was_cuba_hit_by_the_fall_of_the_soviet/