If its going to be several days before the results come back and if they come back high, you might ask your vet if the lab noted any hemolysis. Basically this is where the red blood cells rupture. Sometimes due to sitting around for a little too long during transport or over a weekend. So any zinc inside the cells goes into the serum and can give an artificially high zinc level. Ariel's highest zinc level was a draw done in the evening on a friday and didn't go out to the lab until the next monday. Plus a couple days beyond that before the sample was run due to transport and workload at the lab. So again, I would not rule out that maybe he doesn't have zinc problems. I'm not a vet, so maybe he does. However, its a pretty typical pattern for a plucking bird to stop plucking when on meds. Any kind of meds. Especially those that make them feel even more crummy than the did before. Ariel plucked less when she was on chelation thearapy. She also plucked less when just on Baytril as a shot in the dark treatment. This from a bird that never had zinc poisoning to start with.
So, in light of all that, I can see why possibly the vet thinks its time to give his body a break from the Ca EDTA and try other things. Although, if the Lupron helps, I would seriously have to wonder if its just because it threw his hormones all out of whack compared to normal, left him feeling a little different than normal and diminished plucking. I know this isn't the most helpful post for you. I understand what your going through and it sucks.
Another off beat thought, you might want to ask your vet about children's benedryl. Supposedly, if it works on the bird, it can be a sign that the problem is an allergy. However, its also debatable if birds even have a similar immune response with allergies. Ariel almost certainly has allergies. However, Benedryl did sedate her initially enough to reduce plucking. Then I think her body adapted to it and she started plucking again. It could also give you an idea of how this bird responds to taking medication. If you see the same response from him when given a completely unrelated drug by the same means(oral via syringe or injection) then it ups the chances that his symptoms have nothing to do with chelation at all and more to do with just being given a drug. I'm just throwing out alternate explanations here. All things to run by your vet before trying anything.
Hope I didn't just frustrate you more. As usual for anything plucking related, check for changes in climate and air quality. Before I discovered Noni juice for Ariel, she plucked through the spring, summer and fall but was far more frantic about it on days that either I cleaned and kicked up a bunch of dust, or the A/c was running a lot and blowing stuff around. She was also worse on bath days.
Possibly try some holistic type anti-inflammatory stuff. Easy things you can do at home. Like adding a drop or two of good quality flaxseed oil to his diet. Possibly good foods that have anti-inflammatory properties and if its bird safe and can fit into an overall healthy diet, try to increase those things.
