And he has a point. Consider the timeline of events as we know them:
479: Iuz appears in the northThe question becomes, when did Iuz and Zuggtmoy get together and plot the rise of the Temple of Elemental Evil? The obvious choice is sometime between 479 and 505, which is the only time that both Iuz and Zuggtmoy are both free from imprisonment. However, that carries with it a problem, as the Secret History of the Temple [of Elemental Evil] tells us that Iuz's motives for helping Zuggtmoy were that:
505: Iuz is trapped beneath Greyhawk Castle
513: Horned Society, taking advantage of Iuz's absence, officially breaks away and declares their own nation
569: Battle of Emridy Meadows. ToEE is sacked, Zuggtmoy imprisoned
570: Iuz is freed from beneath Greyhawk Castle
573: Prince Thrommel of Furyondy kidnapped, taken to ToEE
If the Temple triumphed, then he could call upon Zuggtmoy to repay his aid and make sure that Iuz, not the Horned Society, benefited most from the territorial acquisitions in Furyondy. Also, a strong Chaotic Evil ally against the power of the Horned Society could be most useful. (ToEE 29)And there's the conundrum. If the only time that Iuz and Zuggtmoy were both free was before the Horned Society came into existence, how could it be that the Horned Society loomed so large in Iuz's plans?
One solution is that the Horned Society existed prior to 513, not as an independent state, but as an association among the "calculating generals and unholy men at the vanguard of the push against Furyondy" (LGG 62)
This also has great implications for the history of the Temple itself. Before the timeline problem was pointed out to me, I always saw the Temple of Elemental Evil as having a rather meteoric rise over the course of a couple of years, leading up to its downfall in 569. But if we go with this explanation, then the Temple must have been around for many decades, working slowly and stealthily until it felt itself powerful enough to declare itself to the world in the absence of Iuz's support.
But... this explanation still doesn't cover all the issues. Again, the Secret History of the Temple tells us:
Having just learned of the sharp check dealt to Lolth in her plans to wreak Evil, the Lady of Fungi agreed to accept Iuz as an (almost) equal in the Temple. She saw him as an excellent weapon, especially useful against the Horned Society once she had absorbed most of Veluna and Furyondy. She would then encourage Iuz to crush the might of the Society, and she would be left as the great Evil power in the Flanaess, ready to absorb the Wild Coast and Pomarj, while the rumps of Iuz and the Horned ones served as buffers in the north and east. Her hordes, in turn, could concentrate on the hateful elves and dwarves to the west...
And so the alliance formed, and actually worked, but saved not the Temple. Zuggtmoy was bound in its dungeons, but Iuz remained free (just as he had planned).
Another possibility is that it was not Iuz himself who approached Zuggtmoy, but one of the various "false Iuz's" who we are told sprang up following his imprisonment. This doesn't seem very likely, though, as surely Zuggtmoy would have realized that she was dealing with an impostor at some point. Too, the text of the Secret History of the Temple makes no mention of such a thing, maintaining that it was Iuz himself who dealt with Zuggtmoy.
Yet another possibility is that Iuz was able, somehow, to communicate with Zuggtmoy from within the Godtrap beneath Greyhawk Castle. This, however, is extremely unlikely, both because no other such communication is mentioned anywhere, and Zuggtmoy's plans described above seem to assume an Iuz who is a free and powerful agency unto himself.
I confess this is a tough one, and I can't come up with an explanation that satisfies both of the key requirements; a time when Iuz and Zuggtmoy are free, and the Horned Society is a powerful nation unto itself. Any suggestions? Am I missing some vital clue?