I'm still a little lost I guess on this one point I guess.

Sequence 1)JGL first doesn't kill BW.
Sequence 2)JGL does.
Sequence 3)JGL doesn't kill BW.

1 has a point where JGL gets knocked out, then 2 has a timeline where that doesn't happen. 2 happens before 1 in that reality or 1 is never able to happen.

You think the falling off the fire escape in 1 and cut to black and start 2 is a flashback that sets up 3.

But why does 3 repeat that steps of #1 up until the fire-escape, and then divirge? (Or is the narrative switch to BW the reason for the repetition?)

I think the real reason is because the director said (on one of the interviews in this thread) that he wanted the movie to follow JGL and not BW. So having JGL kill BW, live 30 years and become BW, and then go back without the hood should have happened first, but didn't.