Then please tell me how such an article is improved. Seriously now, I have found the article Germanic peoples which uses both systems. Now how should we proceed? Leave them both (which is simply strange for the reader and against the rules)? Put a tag? Ask for the opinion of others? Restore the original one? WP:ERA is pretty vague in this matter. It merely says "do not change" but it doesn't say what one should do if another user changed the system by accident or not.