After you obtain the Black Soulstone is Act II you can talk to Adria and it is several times mentioned that there is already five Lords of Hell in the Soulstone. Who are these five?
To my knowledge there are six Lords of Hell, I think we can be fairly certain that Diablo, Mephisto, Baal and Andariel are all in the Soulstone, that leaves two of of the six Lords of Hell. Belial and Azmodan, seeing as they by that point still haven't been fought surely they can't be in the Soulstone. Is this an error by Blizzard or is there some Lord of Hell that hasn't had a good pr guy?