Well, on the subject of using original material to help comeback, I did the opposite.
I concentrated on mainly The Balanced Embouchure and a few supplemental exercises from more "modern" materials (compared to my original approach). While, I think, I based things on my original teaching (my teacher studied with Schilke, so that whole "wind", Chicago thing), I went beyond that in development materials.
I went from struggling with High Cs and a workable A above the staff to a workable E above High C with a playable Double High C.