Originally Posted by Fly AA J all the way
You just answered your own question. KUP does book into P, which means that a YUP (more expensive) books into A.
I thought I read the KUP has replaced YUP, or that they both book into P, but I guess I am wrong.
Anyway, $1,000 one-way for STL-SFO should get you into first without needing stickers.