I'm at the very beginning of the Kingsparrow Island mission. I choked out all the guards at one of the entrances, went to grab another rewire tool from a stash by the waterfront, and when I came back every single guard post had a new guard at it. Do they just keep on coming? Do they really respawn infinitely each time you leave the area? Or will they stop eventually if I keep piling up the sleeping bodies?

Hmm.... sounds like a glitch. I choked out most of the guards, and they never re-spawned. There was one point
where additional patrols arrived, but that was part of the level's design.

When they respawned on me, the old unconscious bodies were still where I'd left them. But all the previous spots where the guards were had a guard there. There wasn't enough time for them to patrol from inside the fort to those spots in the time it took me to stash that one body and come back. We're talking like ten seconds.

So it's starting to look like I've got new spawns of guards rather than guards from elsewhere pathing into a vacant patrol area.