Stack Exchange has wiki-like features specifically to handle the case where an answer is longer relevant or true and can be updated with new information:
Stack Exchange was specifically designed to adapt well to rapidly-changing events. That's why it has Wiki features. Like Wikipedia, we are not content to wait for the first historians to write the book. We're happy to answer questions in the context of what is true today, knowing that as facts change, the answers can easily be edited or replaced.
Simply edit the answer (or, if you don't have enough reputation to do so, suggest an edit) with the correct, up-to-date information.
Comments are ephemeral and are meant to help clarify and improve the answer: you can ignore them if they no longer do that. I'd go one step further and flag the answer for comments cleanup by a moderator.