I thought I would regale my experiences with dust and the new iPad in case it is helpful to the OP.
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I bought mine the day it released, and as soon as I got it I noticed a single speck of dust under the screen. It was in the middle/lower half of the screen and a bit irritating but I just didn't feel right about returning over that so I ignored it.
Then, last week I was installing a screen protector and I noticed that there were actually 2 dead pixels I had never noticed on the screen! With these pixels and the dust I felt justified in returning the iPad.
I scheduled and Apt with the store and told my story to the employee. He was understanding and had no issues with swapping it out. He went to the back and returned with a nondescript brown box with a solitary iPad in it. I assumed it was likely a refurb since it was not a retail box.
He said he wanted to make sure I was 100% satisfied (nice customer service) before I left, so while I was still there I checked it for dead pixels and didn't see any. However, I felt uncomfortable standing there making the guy wait while I further inspected the unit so I said it looked good and took it home.
Immediately after walking out I noticed that there were some scuffs on the back of the unit. Some colored marks that did rub off, but some very small scuffs that did not. I was annoyed but assumed it was a refurb and again, just decided to ignore it.
The next day however, I took a light to the screen to check for dust. I spotted a speck, and then another, and another, and another...and so on. There was a TON of dust under the screen all over the place on this replacement unit. I took a painting app and started circling the dust spots. After I hit 17 I stopped circling and went to the Apple store after work.
The 2nd time was not nearly as smooth. I did not have an apt so I had to wait a bit, and I had to explain and display the issue to 3 different employees before they huddled around for a resolution.
Again they said they would replace it, and after a lengthy process of trying to get a record of my replacement from the day before they brought out a brand new iPad in a retail box. They cut open the plastic and gave me the new unit.
Again, I inspected for dead pixels (none) and this time I looked it all over. The back looked fine since it was new and I did not see any dust under the screen when checking all over with my flashlight. It took a few trips and some waiting but in the end I was very satisfied.
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Now, how my experience pertains to your particular problem:
I too wondered if it was possible to get a device with 0 dust under the glass. And while I'm sure it's possible (as mine either has none or too little to be noticeable in a quick inspection) I would imagine it is very rare.
However, I would say that a small amount of dust, if inconspicuous enough for the owner to ignore, is probably acceptable. However, there is a limit and from what you've described as your quantity I would say you've hit it.
I wish I had brought my device in within the return policy window because if they had they had a problem with swapping it, I could have just said I wanted to return it and then bought a new one. I felt worried that since my device was 3 months old I might have issues returning over small niggles. If you are still within that window I would highly recommend swapping it out for a better unit.
If you decide to go have it checked out I would recommend to circle all the dust as well with a painting app. It helps show them quickly the magnitude of the issue, as well as aids them when they inspect them to verify there is dust underneath.
Again, it comes down to what you, the buyer, feel is acceptable. If you don't feel your unit is acceptable than you should return it until you are happy - it's your money. Good luck no matter what you do!