Barry Burton mentions that the Revenant was not in the Brief. This is most likely because the information he received was based upon Claire Redfield's account from her experience on the island and Revenants were not roaming the island yet.
Some Revenant, if not most, possess a vestigial third arm, seemingly sprouting from the right arm. It is unknown where this third arm came from. That said, most Revenant seen inside the preservation chambers in Episode 4: Metamorphosis are missing this third arm. Neither Barry nor Natalia mention this detail.