The stairs in the article are probably not code compliant, even with all that work. The uppermost tread is cut short. Most locations require all treads to be the same depth, so his half-tread probably won't pass inspection.

The stringers either need to land a little further away from the wall, or the stairs the need to be at a slightly steeper angle (but check local building code for the max permitted angle!).

I built stairs with a friend years ago, and there are a lot of constraints to solve for if you want to build code-compliant stairs. A good parametric CAD system was very helpful. We could specify overall dimensions: stair rise/run, number of treads, thickness and width of the stock. It'd solve for the critical dimensions to verify, like tread rise, stair angle, tread depth, and the angles to cut the stringer ends to.