From there I found a lot of free stuff on Sharecg. I have this staircase in my library as guy91600. You have to look for it to see if it's still there.
https://sharecg.com/b/21/DAZ-Studio/?keywords=guy91600&s=dd&member_type%5BAll%5D=on&pn=1

Ah. I figured it out. Ya. I got my copy of the staircase from Sharecg too, but not from guy91600. I got mine from Endoen: https://sharecg.com/v/9699/ .

I also have a vague memory of discovering guy91600's version of it later, and wondering whether this was infringement between guy91600 and Endoen.

Eventually, I replaced the Endoen staircase with my own, making one from scratch in Blender, because I wanted to offer it as part of a free model for others ( https://www.deviantart.com/luqu/gallery/68374961/vehicle-oct-ufo ). But I finally decided against all staircases in favor of an elevator/lift - for wheelchair access.

I'm sorry I couldn't help. The stairs I used were free and that's good enough for me.
I appreciate your thinking of people in wheelchairs, and I thank them on their behalf.