Hopefully I'm making a mistake and a reader will point me in the correct direction.
While looking for handwriting samples for Daily Genealogy Transcriber, I run across a variety of items. This image is part of a declaration of intent in Delaware County, Ohio, that was marked "CANCELLED."
The direct link to the image is here.
I decided to try and locate this "cancelled" naturalization in the index at FamilySearch.
Several searches were conducted of these records, including a search for the first names of "david arthur" in Delware County, and all Lewis entries in Delware County. The "cancelled" entry was not found.
Searches were made for four of the names immediately preceding the "cancelled" entry. None could be located through a search of the database "Ohio County Naturalizations 1800-1977."
There is no indication on the search page that this index does not search all the counties that have images and there are some results for Delaware County, Ohio.
Lesson: Do not assume the index is complete and perform manual searches if you have good reason to believe someone should be in a series of records even when they are not in the index.