I suspect he ran into the infamous '90%' problem: he did the first two and the final end-stage and wrote it down nicely, which took 90% of the time & energy he

I suspect he ran into the infamous '90%' problem: he did the first two and the final end-stage and wrote it down nicely, which took 90% of the time & energy he had, then looked at the difference between the last two and realized that it'd need another like 5 images+explanations and that would take the next 90% of the time... which wasn't going to happen, so he posted it as-is FWIW.