Because the site is dynamic, it does not build HTML files for each different version of an article. Instead it generates a "permalink" for every version of the article. It does this based on the article's versions frontmatter.
For example, an article that is available in currently supported versions will have permalink URLs like the following:
/en/github/getting-started-with-github/set-up-git/en/enterprise-server@2.22/github/getting-started-with-github/set-up-git/en/enterprise-server@2.21/github/getting-started-with-github/set-up-git/en/enterprise-server@2.20/github/getting-started-with-github/set-up-git/en/enterprise-server@2.19/github/getting-started-with-github/set-up-git
An article that is not available in Enterprise will have just one permalink:
/en/github/getting-started-with-github/set-up-git
If you are a content contributor: You don't need to worry about supported versions when adding a link to a document. Following the examples above, if you want to reference an article you can just use its relative location:
/github/getting-started-with-github/set-up-git