I'm working on edit #3 of the new Sgt. Dunn Novel, SS Assassins. Found a few things that were the result of the length of time it takes to write a book. You write something early in the book, and kind of "forget" you did. This can result in saying something else about the same thing.
The best one was in reference to a house. In an earlier chapter I said it was built in the 1500s. Later, I specifically state it was built 41 years ago (which of course, would be 1903). Glad I found it myself. Stayed with 1903 and fixed the early reference.
Now back to work, lad. As Saunders would say.