I should share a bit of my writing process here. Before I started scripting, NevermoreFox(aka the competition) and I passed a lot of messages, fleshing out the, well, results. The costumes at least and a little bit of what happens in it.
So then I start writing and the only thing I actually had in mind where a few panels in pages 20-21. The rest were open and I just let my mind wander and sketched the story as it made sense to go.
Sometimes, I'll go back and rewrite things in earlier pages to give more foreshadowing, but most of the time, I've included enough hooks to work off of so I don't have to worry about it.