Hun, I haven't read back on your thread, but I have been thinking about you and B a bit. I really feel for you as Z never consistently STTN from 4-12 months. We would get 1 week bursts, then back to NW

Is he still on probiotics? - these did seem to help us a lot, we started around 11 months.
Do you think that having him in our room could be possibly disturbing him? I find Z is a super light sleeper and if 'woken' rather than stirs on his own, he is awful to get back to sleep. Dark room, not too hot, white noise and crazy consistent routine is what helped us at this age
Can DH settle B? At 13 months we did WI/WO for the first time. It sucked. DH had to do it, and obviously we had to both agree Z wasn't in discomfort. Since then he has actually become a pretty good sleeper. Still NW with teeth, and I do think part of it was that he grew out of the NW and his body just matured. BUT it did happen and he STTN most nights now.
There is hope! as you can see I never thought Z would get there but he did. B will do it....in time. So many hugs