Proving no Naturalization

Yesterday I called the District Court of Utah to see if they had a record of Naturalization for Dominique. The very helpful clerk looked through the old files going back to the late 1800’s. He didn’t find Dominique’s naturalization. But afterward, he searched around on the internet and found him in the 1880 census. That was the census that did not collect naturalization data, and I’ve already searched it. But it was very kind of him to go the extra mile and try to find my ancestor. He is sending me a letter on official letterhead stating that they have no record of Naturalization for Dominique. I may end up just getting as many of those letters as possible. I have an email from NARA, but I might be able to get them to send a written response.