They don't have enough information to make a 3rd season just yet. If they decide to make a 3rd season, you're best bet is it'll probably come out October of 2016. Following suit from season 1 and season 2, they roughly take 100 chapters just to make 25 episodes. THEY could go the alternative route of only doing 12 episodes (like a lot of series are doing right now) which would roughly take 4 chapters per episode, but I doubt that would be the case.
As far as SnB the Anime series, what the animation director said could be taken is several different ways. He could have also meant that the 5th OVA was the end of the Valefor arc, but didn't say it was the end of the OVA's in general. Also, I would like to make mention that the Anime adaptation for both don't exactly do the Manga justice, especially when they throw things into the series that have no correspondence with the series at all.