Going through the level's signs revealed that I'd missed talking to the genie. And the NPC at the entrance to Defaultton has different dialog when you're leaving. So I took care of those things. This should now be a 100% playthrough, disregarding one extremely hard to reach filler screen that I'm sure was meant to be invisible on the map.
There's also a sign informing you you can't enter the maze without the map. Didn't try going there without it, so I didn't get it. And there's an unused sign that was going to explain the colors you're allowed to land on in that one challenge. It was going to be placed in the challenge itself, but I guess Lucinda decided to hide that information somewhere else instead and rewrite it to be a bit less straightforward. And the moon behind one of the wrong dungeon doors says "LOL," which I can't see now.