During PTAB patentability proceedings, the Federal Rules of Evidence are applied. And, while the USPTO’s definition of a “proceeding’ includes the preliminary proceeding (i.e., petition filing, preliminary response) it is important to keep in mind that the the trial Order is not the final word of the PTAB on patentability; it is simply a preliminary gauge of the merits prior to trial. The “trial” itself does not actually begin until after institution. As such motions by the Patentee that are directed to perceived evidentiary defects of the petition are deemed premature prior to trial institution.
This issue is often raised in the context of printed publications accompanying a petition to the PTAB for a patentability trial. While patents are considered self authenticating by the USPTO, publications can be considered inadmissable if not authenticated (and perhaps hearsay as to undated submssions) by the petitioner. But, the PTAB has set the time to challenge such evidence post-institution via a motion to exclude.