using odd but inconsequential details from previous books to build in new story arcs, motivations, and connections in new stories. If you read some of his short Dresden story collections, the ones where he writes some intro, a lot of the time when he's trying to build stories that have some connection to Harry's world, life, and events, he often latches on to a figure there, a small detail here, and then expands them and works them back into a new Dresden narrative.

I have never read about Butcher having the Dresden story all mapped out from end to end, but that doesn't mean that he hasn't. I just have read about his process and how he likes to go back and find things in previous stories and use them again to add depth and continuity.