That's wild! It's kind of nice, but also a real bummer to hear from someone else who developed this madness through chronic dislocation. Despite what I've read in medical literature, talking to doctor's you would think it's about as common as people being bitten by werewolves.

I'm glad you got the labrum work done. MRI with contract (arthogram) was something I was going to suggest to test for an overlooked labrum injury, which is a not uncommon cause of this kind of pain and dysfunction.
Did the issues develop while healing from the surgery? Laymens guess from a fellow bum arm, however you were holding your arm pre-surgery plus while weakened after surgery could have put a lot of strain on your neck, levator scapulae, etc, pinching/irritating the nerves.

I know my winging scapula started to develop from the dislocation stretching and pulling on my long thoracic nerve, coupled with holding my arm up protectively and using my neck muscles to lift it instead of my back.
(It popped out multiple times a day for almost 2 years and got so bad I would dislocate it trying to get dressed or scrubbing myself in the shower.
It got Gross! One PT dry heaved when trying to do the maneuver to pop it back in and my arm just fell in to place and popped out the back with no resistance. Sounded like putting a truck in to gear, Hahaha!)
When I finally got surgery, capsular plication, to cinch that sucker back in there my nerve problems got WORSE because my neck was again forced to do all the work, and my arm was pulled forward by the sling. 2 year of holding it up with my neck and I couldn't let it go slack in the brace.
The doc even anchored my shoulder capsule to my scapula to stop the winging.. but the body finds a way and the shark fin is back.

If you can find someone to do it, it may be worth trying to get the EMG again. Did they just test your arm, or did they put the needles in your ribs and upper back as well? It took a literal yelling argument with one of my Dr's to even get them to test the long thoracic nerve, which is a hard one to accurately test. Even if they do, most EMG's seem to just test for "ON" or "OFF" and not measure any level of dysfunction in between. Which, as you seem to be experiencing, leaves a lot of room for issues. There's a lot of people on here who mention multiple failed EMG's, only to have them re-done years later and show major issues that were missed and Could have been fixed if only someone looked a littler harder.

Keep an eye on that shoulder dent. Especially if you PT mentioned it could be from a weak upper trap. That would be a major contributing factor you the pain in between your shoulder blades, meaning your rhomboids are working double due to the weakness of your upper trap. I'm fighting this same battle in PT now. It's hard to get the balance back if your nerves aren't sending a strong signal to the muscles in that area, and hard for the PT to tell when you're compensating with rhomboids or using your trap.
And that dull, tennis ball like ache in the arm pit my PT says is my serratus anterior muscle basically endlessly spasming. If you still see you PT, maybe they can help focus on that muscle to get you some relief.

I hope you keep pushing to get someone to take this jazz seriously! It helps a lot to go in to the Dr's ready to guide them in a new direction, rather than letting them guess and send you through another round of unhelpful PT.

Here's a few more articles for your perusal:
[Edit- ugh, it won't let me submit links yet]


Also, getting TMJ treatment with a special TENS unit (delivered some other kind of shock than the usual) from my desist has helped A LOT, although the relief if temporary, it calmed my cramping shoulder down.