The Board observed that the “Wayback Machine” suffers from a serious evidentiary flaw: even Petitioner noted that the “Wayback Machine” shows “each date on which a website has undergone a significant change.” “What may be insignificant to the archivers for the ‘Wayback Machine’ may have significance from the standpoint of evidentiary value in a trademark proceeding.”
It’s not just that. In a recent case, we considered the use of such material, and on due diligence were informed that even a given page in the Wayback Machine is not definitively made up only of HTML that was present on a given website on the date claimed. We were given to understand that gaps are “filled” in later, or with earlier files, or that there can otherwise be mixing and matching. In short, this is a phenomenal research tool — but hard to authenticate for purposes of retrospectively proving what was on a website, when.
UPDATE: Here’s some scholarly thinking on the topic.