Also, another thought: why isn't there an index at the back of adventure modules (especially longer/mega ones) to help you find relevant info?
In the adventure I'm writing now, this is something I'm being very mindful of.
NPC roster index (name, location, appearance, voice), treasure roster index (description, location, value), monster index at the start of each section (monster, location, paginated reference, XP value) - these are the big items I'm appropriating to facilitate ease-of-use.
The NPC index is handy so you can recall at a glance who does what and what they're like (my dungeon has about two dozen NPCs, so it would be tough for a DM to remember which sections are controlled by whom, and where someone is when the players make reference to them and they need to be looked up).
The Treasure index is handy for those common scenarios when the party decides to finally investigate that potion they found five sessions ago and you've already forgotten what it does, or when they go to sell that platinum bracelet and you can't remember where to look to find its value.
The monster index I find is helpful in planning encounters or patrol routes, knowing at a glance how deadly the upcoming area is, getting a quick and easy answer for "where's the stat block for this thing?", and also to know which areas to fill with signs of the creature's presence (harpies in Area 17? I suppose I could put some feathers and broken egg shell bits in Area 16, and some harpy poop in Area 18).