A failed rotator cuff tendon repair is usually defined as one that has torn all the way through the tendon again. This is called a full-thickness defect. Your experience is not uncommon. Studies report some question about how much tendon healing is linked with pain relief. Patients with poor tendon healing can still get full pain relief. This means that the symptoms are not an accurate gauge of tendon healing.
The primary difference you are likely to notice is in the area of strength. A complete repair is needed before you can get back your full muscular strength. Strength also depends on muscle quality and how much fat has filled in and around the muscle fibers.
It’s also possible the rehab program can make a difference in outcomes but this remains an area of study at this time.