A said:
Tennes. There's the 'Tennes' witch in MoI, but we never actually see it used directly. Interestingly, Tennes isn't even listed in my glossary of tBH (mass paperback edition with the lone double-kethra-knife figure).
Another interesting one: Envy in MoI says she used Poliel's warren to cast disease into the Pannions, but we never hear a name for Poliel's warren or hear of her plague being used by a warren in tBH.
Finally the biggest mystery -> Kurald Thyrllan and Kurald Liosan
Generally it appears that Kurald Thyrllan was the old warren of Light used by the Tiste Liosan, and that they left it and isolated themselves in Kurald Liosan, which is much more... 'sealed'. This comes from HoC when Onrack talks about how they've never seen Tiste Liosan, even though the T'lan Imass had often traveled through Thyrllan. Additionally, the warren Pearl and Lostara travel through would be KT - wherein resides Osserc's avatar but not the Tiste Liosan themselves.
However, there are some random references scattered about that would imply that Kurald Liosan is the true warren instead. I know there's one about 2/3 of the way through RG. I'll try to find it...
Strange that only the Liosan would have 2 warrens. I'm theorizing there is no Kurald Liosan, just Thryllan. 1 Elder warren for each Tiste race, the Imass have never seen Kurald Liosan because it doesn't exist to be seen.
Still, if you find the quote supporting the existence of 2 Liosan warrens, I'd love to see it.