I *just* inadvertently figured out a different way to solve the problem for my stairs that have two landings between the two legs of stairs and corner at the first landing:
I created the top end with the specific number of treads, then a single tread 'stair' that I adjusted to the upper landing length, then the bottom end of the stairs with the specific number of treads. After tugging them into place, clicked for a landing.
It only took me a year.
Yay!