Seriously. I've never needed a written outline for much of anything. Even my years long d&d campaigns, and the radical changes that interactive stories like that bring, I don't have trouble keeping things straight in my head.
The only thing I do keep like that is a timeline of past events as "canon" to keep exact dates in place. I think of it as the inverse of an outline.
If I skip ahead for a section as I'm writing, it's easy enough to just pop open a second file and make a note for bridging ideas.
I'm not saying outlines are a bad thing, they just don't work for me. Since they aren't a necessity, I don't bother with them. Even with my three ongoing projects, and my slow-ass writing pace, I haven't lost track of anything yet.