I have been continuing to do light stretching exercises on my own every day. I do the ones that were prescribed by my physical therapist, and also just try to stretch the shoulder in all directions. For example, I'll reach over to my right shoulder and try to get my hand as far around to my back as possible without causing too much pain. Or I make an effort to reach into my left back pocket and see how much I can stretch while doing that.
My biggest effort has been towards getting more external rotation back, and it seems to be working. I have two exercises for that. I hold a wooden dowel in front of me with my elbows at right angles, as if I were holding a tray in front of me. Then I use my right hand to push at the left hand. I try to keep my left elbow moderately a bit close to my body, and feel the stretch in my shoulder. Another variation of that is just to try to externally rotate my shoulder by keeping my elbow pinned at my side, bent at 90 degrees as if I'm holding a mug in front of me, and then moving my hand out to the side in an arc parallel to the floor, as far out as it will go. It hurts and doesn't get very far. But I've noticed in the last two weeks that it is actually moving more and more over time.
I went away last weekend, and while I was away, my shoulder was kind of acting up. It got a bit painful and weirdly sore. There was a strange pulling sensation somewhere, as if I had a thread coming loose in there. Hard to describe.
Anyway, this evening I was shampooing and suddenly thought "hey, my hand just went farther over my head than it has in a while, I'm sure of it!" So I took another measurement. My last measurement was last Friday. My hand can move an inch farther up the wall, and over an inch more out in external rotation than it could last Friday! Wow, I am very impressed. I have no idea whether this is because I stopped going to the fairly brutal PT sessions, or whether this is just the natural course of the disease. What good progress!