Permalinks of posts with numeric slugs can sometimes look to WP_Query::parse_query()
like a date archive, as when your permalink structure is
a post with post_name '05' has the URL
This function detects conflicts of this type and resolves them in favor of the post permalink.
Note that, since 4.3.0, wp_unique_post_slug() prevents the creation of post slugs that would result in a date archive conflict. The resolution performed in this function is primarily for legacy content, as well as cases when the admin has changed the site's permalink structure in a way that introduces URL conflicts.