Within a chapter, foreshadowing is essential. I’ve have a revision pass I call “That can’t happen — it happened.” I think it helps to frame the issue this way so I can be sure the start of the chapter sets up the end of the chapter.
(It goes after the “And then the murders began” revision.)
It’s essential for me to assure the chapters have a self-contained story arc.
There are a few things setup in The Forge that are part of The Sword and Crystal. They were essential parts of the series, and worked out well.
In The Crown, The Orb, and the Scepter, I've uncovered a problem that’s also essential, but has no real foreshadowing anywhere. It’s a kind of whoopsie. While I hate to modify The Forge, I really, really need to set this up or the overall five-book arc isn’t going to work out well.
It’s not a big change. But it’s necessary.