Let's say your parent article has versions.
When you first create a synced article (which is always a child), none of the parent article's versions display in the editor while the article is in a Draft publishing status.
Once you publish the child article, the parent's versions display in the child article.
Activating a new version in either the child or parent will automatically update all other synced articles in this relationship to use that active version.
If you stop sharing content between the parent and child, the child article will lose all versions except the current active version.
Versions behave and display in parent articles just as they do in un-synced articles.