I too never saw your first request, but this is my story:
My son was diagnosed with torticollis at 2 months old. He had had a hematoma on his neck from birth. I guess because they had to use a vacuum to pull him out caused it it, I'm not sure. He didn't have the arching that I can recall.
Anyhow, we went to PT for about 9 months. He got better. We moved cross-country and didn't think anything about it. Didn't continue the exercises, weren't told to, he was better and didn't think about it.
Well, at about 3 years old we noticed he was doing it again. Not sure exactly when he started tilting his head again. We took him tot he doctor. They set him up for PT, had his eyes checked, etc. Nothing worked. We would keep going back to PT and finally when he was six he had the muscle release surgery and then PT. He's fine how. We still had to remind him to hold his head straight, because he's mostly only known the tilt and he thinks that's straight. It's been two years now and he's fine. the only thing is is that his ears are uneven and for a while his eyes were uneven on his face, but the eyes, I think, have adjusted but the ears have not. It's hard for him to wear sunglasses and stuff because they're always tilting from his uneven ears.
I would advise to keep up the PT if it's working and the home exercises even if the PT says you don't have to and if the tilt comes back to get it looked into right away and then maybe you can avoid the surgery. I think that if we hadn't moved and our lives hadn't changed by moving cross-country twice, then maybe I would've noticed it sooner the second time around and we would've avoided the surgery. His muscle was so fibrous that the PT wouldn't do anything. That's when he had to have the surgery. Luckily the PT and surgeon we have here were very good. I got a different PT then the first one we had at three years old (the baby PT was excellent too) because he didn't do much with him, I had to do the work and I didn't feel like I was doing it right. And we only had a couple of appointments with him and that's it. I shopped around for another PT and found one who is excellent and anytime we need PT for anyone in the family, we go to see him.
I wish I had thought of chiro then, it does wonders too. Not sure if you can use this method on babies, but it's very gentle to me, it's using an arthrostim rather than manua; adjustments and I like it a lot better than manual adjustments. Not a lot of chiros use it though or are good at it.
Good luck and I hope it all works out and you find ot about the arching.