As I mentioned previously, I've been checking my progress a few times each week by testing my range of motion using a few simple measurements. The last mark I made was on March 22, a week ago, although I did make a few measurements over the course of the week and found no gains.
This evening, I clasped my fingers around the back of my head and felt like my left arm was moving a little more freely, with less pain. I went to my "measuring stick" taped up to the wall, and sure enough, the tips of my fingers could go about 3 inches higher than on March 22. I'm pretty sure this improvement happened in the last day or two.
It's really amazing and feels incredibly good to make such progress all of a sudden, even if it is just a few degrees change.
On the downside, I tested external rotation and there's still no change in that.