Ask HN: Are companies required to keep an archive of their Terms of Use?

When you use an online service, you either explicitly or implicitly agree to their Terms of Use and other legal documents. However, since the service can change these documents at any time, how would I, as a user, prove that they added terms I did not initially agree to explicitly when I signed up? How does the service protect themselves from users lying that there were certain provisions in the documents in the past?

It seems like you wouldn't be able to do any of this without an auditable log of the service's legal docs.