Helldritch
Hero
Lanefan is quite right. I've run the Temple of Elemental evil over 20-25 times over the years with different groups and only four ever found prince Thromel. Not all magic items were meant to be found. Some were so well hidden that if they were ever found, I would get suspicious and start wondering if one of the players might not have the adventure at home (this is one of the problems with published adventures. Your players can buy them too without your knowledge).
Once I had a strong suspicion about a new player so I changed a bit of the adventure and modified the maps just enough to fool the player into thinking the adventure wasn't tweaked. Guess what? He fell in the trap and then I knew that player was cheating. He would search zones that were no longer there and was startled when a new zone was found but not on the original. I had a long talk with him and we agreed that in adventures that he personally owned, his character would take a back seat. I would ask him before any published adventure/campaign if he had it and we would both act accordingly.
Once I had a strong suspicion about a new player so I changed a bit of the adventure and modified the maps just enough to fool the player into thinking the adventure wasn't tweaked. Guess what? He fell in the trap and then I knew that player was cheating. He would search zones that were no longer there and was startled when a new zone was found but not on the original. I had a long talk with him and we agreed that in adventures that he personally owned, his character would take a back seat. I would ask him before any published adventure/campaign if he had it and we would both act accordingly.