Actually, in For Good (at least with Cheno and Menzel) it changes back and forth as to who is on the higher part. At least it does in the special features from the PBS Broadway special. I took special note of this because I always assumed that Cheno would be singing the higher parts, but that's not the case. Now, I don't know if this has changed since that video was done or if it changes depending on the actresses portraying the roles.
Regarding the last note in I'm Not That Girl, I always thought the note that was written sounded strange and anti-climatic. I think it makes the song sound like it's not over. I've gotten used to it, but that was my initial impression.
". . . POP . . ."