Comment by mikepurvis

Agree with the sibling comment, but a starting point is also just to write docs for your future self, which is usually going to be type 3 or 4. Most of us who have been programming for a few years have had the experience of being mystified by something we ourselves wrote in the past, so it eventually becomes fairly straightforward to predict what kinds of things future-me will need a hand in piecing back together.

And it turns out those kinds of docs are pretty useful to my colleagues in piecing it together also.