According to my research, the results on stem cells for rotator cuff injuries are mixed. Rotator cuff tears are widely variable as there are several involved. It appears that if you have a complete tear, at this point surgery is the best option. Here is the best research summary I found today:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6333521/
Their conclusion probably best describes why insurers don't yet cover most stem cell therapies: "Although there is considerable interest in biological augmentation of rotator cuff repair, outcome measures have thus far been mixed. Our review of the literature suggests that the method of delivery (for biologics as well as cells) may have a considerable impact on success. "
I too was hopeful - except that I have a full tear at the top of my shoulder - so it is being surgically repaired this month.