I've also seen NYT and CNN make updates to articles that materially change the original reporting without noting the change[1], or adding an blink-and-you'll-miss it note at the very end of the article. Ars consistently updates the title and has the explanation for the changes before the original article body, which is beyond other news organizations since it's impossible to miss.

1. See the NYT or CNN tabs at http://newsdiffs.org to see how often this happens