After two days of no feedback by the community at all, and a confirmation by my co-moderator Ninefingers, I merged scope into allowed-questions - these mean as much as "What is on-topic on Crypto.SE?".
closed-questions is a bit different, it means "Why was this question closed?".
(As long as there are no tag-wikis for meta tags, I'll let this post here be the "definition" of these tags, making it community-wiki to allow editing. Feel free to post a separate question and provide an answer for all tags, though.)