Your experience reminds me of the time we called Professor Nikolai Bogduk, consultant physician with an interest in musculo skeletal research at Newcastle University. My client was using morphine for neck pain, the insurer said he was drug addict with no pain, we said he was allocated 15 doses a month but never used all of them,only what he needed, and his pain was real.
So Bogduk injected local anesthetic into a tiny neck joint he thought the pain source, using a fine needle. The pain vanished, the neck became completely free in movement, but only for the expected lifespan of the anesthetic, whereupon pain and restricted movement returned. Joint pain source identified and confirmed. Case won.
Bogduk referred very unkindly to others who injected a freezing solution into joints using a needle he compared to a thick six inch nail to perform a similar test.Sounds similar what you endured,twice. Your procedure is of course different, to deliver more product to a larger space.
The approach sounds like trial and hope. I hope it works this time. The stenosis sounds severe, and to my uneducated mind,to be mechanically causing the nerve embarrassment.