Is it normal to filter out nearly 25%?

I am running a search for Mohave County, AZ and there are 46,307 total DataTree Owner Records which I broke down into 158 increment groups. Then I download increment groups 1-56 which was like 950 results.

Next, I downloaded increment groups 57-100 which were about 5000 results. The total I was trying to download was about 6000 results.

But when I combined and opened the files, there are only 3800 results after removing duplicate addresses.

I noticed that I have 1485 free records to download, so I'm guessing this is all factored in but is this normal?

And on a related note, what is the best way to avoid possibly downloading duplicates in the first place?

Thanks!

Ed