So I am curious... I was doing the Regent Mission last night. I was taking a loooong time, because I did not want to trip any alarms, but I also wanted to loot and explore. So first things first, I took care of the Regent (nonlethal method). Looted his chambers and all. So I spent the next couple of hours moving around Dunwall Tower, avoiding notice, choking out guards one by one, lugging their bodies to a hiding place. So yeah, a good section of time was spent jumping from chandelier to chandelier, waiting for patrollers to position where I needed them to be to time my choke and grab.

I took out one patroller who would pace the upstairs corridor muttering and occasionally go into the bathroom/whale oil room. Took him out, zipped away with the body and waited for the one guy who would occasionally path into a doorway, then away. Well, a few minutes later, another patroller, doing the same path as the guy I had choked out, popped up. Grrrr. Took care of him. I got him a third time (in between, taking out a different guy and stuffing him in a closet.) Finally, after three patrollers on what seemed like the same path, I finally got to a point where that area became permanently clear.

So - as some guards are taken out, is the AI smart enough to switch someone from another area to add to their patrol or change it? Or is the game effing with me, as it was annoying and tense to figure "OK, this section is clear, now let me get the middle guy, before tackling the musical overseer/dog combo at the other end..." only to find out I still had pathers to take care of.

I did end up with quite a pile of bodies in a stairwell and another in a store room. Heh.

I can't say if it's the intended effect or not, but yes, Dunwall Tower was one of the places for me where the guards
seemed to "refresh" after a while as I took the already existing ones out. It stopped eventually, but I was completely
out of sleeping darts and getting pissed off, - especially those music-box toting Overseers and dogs, grr.

I was wondering about this too. Harvey says the guards change their route. There were so many guards in that mission. I took them out before finding the Regent and it took a long time...snoring guards were everywhere. I was detected a lot and I still think I missed a lot. It's ok, the next run will be more thorough.
http://www.gamesas.com/topic/1418287-stealth-info-somebody-should-be-on-duty-here/

Thanks, I am glad it wasn't just me then. I was being very careful, so it was annoying to feel like "ok, that corner is cleared", only to have the same looking NPC, doing the same pat.

My other beef in that seciton - spoilers... is The Torturers Room.

Occasionally, when a guard paths near another guard post and sees it vacant, they will take over the vacant guard post/patrol path. That actually makes it easier to clear guards out of some large areas. I too knocked out and stashed every single guard in the Dunwall Tower mission. It took forever. But, I found one area that has a couple of patrols go past, and nothing between myself and my body-storage room. So I'd go up, nab a new body, stash it, run back, then wait for another to path by. Rinse and repeat.

But it can get annoying in some areas. In the final level (the lower portion), I've had guards just pop into existence when I go far enough away and come back. New guards taking over the old posts, while no other posts had been vacated. I had to clear out some whole sections of the level three times before guards stopped showing up. Soooo many bodies piled up. All snoring.