2008-04-01 : If a split card is turned face up, the ability counters all spells with the same name as either side of that split card.

2008-04-01 : The last ability counters all spells on the stack with any of the appropriate names, no matter who controls them.

2008-04-01 : The only cards you turn face up are the cards exiled with the Grimoire Thief that was sacrificed.

2013-07-01 : Once a player gains control of Grimoire Thief, that player can look at all cards it exiled, even if those cards were exiled while someone else controlled Grimoire Thief.

2013-07-01 : Once a player is allowed to look at the exiled face-down cards, that player may continue to do so even after Grimoire Thief leaves the battlefield or another player gains control of it.