I've seen several mentions here of the lack of border control in Andorra, and indeed, I saw none when I entered nor when I left. But a web search finds a lot of pages stating they do maintain border control and none (that I saw) saying the opposite.
Several source make Monaco, San Marino and the Vatican City "de facto" members due to reduced or no border control, but when I tried to add Andorra in Wikipedia, it was reverted on the grounds it needed a citation. (though the citation for the other three is a 404.)
Anything official for Andorra or the other three?