Got a quick look around before the weather turns
Re the holes for the supports in terracing. They were there all along. They double up on their use/position. Initially, that's where the temporary barriers were fixed. As the barriers came away as they moved up and down they left holes behind, a couple posters spotted them. I made a guess as below that they might re-use them, which is clever and efficient sequencing. There is more chat on it amongst other pages.
You know, it wouldn't surprise me if they lined up the prop positions, so they attach to the very holes in the new terracing left open where the temporary barriers were fixed to.




