As you’ve probably guessed, the PCs were supposed to find the orrery (or the Flamma Horacalcum, as it’s actually called) right at the start of their exploration and then see all the visions. The way it happened here is a little more awkward narratively but still worked out. In the forums the module writer says he originally placed it in the main throne room, then moved it to a side room to reward players who like to explore. Now, I don’t know any experienced RPGers who don’t explore every nook and cranny of a dungeon searching for loot, but let’s say they do exist; I think it’s still a bad idea to put something that conveys so much narrative in an out-of-the-way place. It should have stayed in the throne room so that the players can see it right away and take it with them. If they don’t take it, at least they miss out on the narrative because they chose not to take the obvious magic item, not because they searched the rooms in the wrong order. Or maybe just make it so they don’t need a specific item to see the major visions. Obviously the module writer disagrees with me, but I think that if you’re going to spend time coming up with important backstory, you shouldn’t be hiding it away.
Oh, and I’m also worried that the party’s being given a second major artifact, after the Sihedron, before they go and face the final bad guy. Could we try to make that fight a little bit difficult?