A cousin graciously shared with me a copy of a casefile a relative had shared with her. I was very glad to get it.
The relative of the cousin received the file from the National Archives years ago. I wondered if the National Archives had sent her the entire file as it looked like the original copies were made in the days when mail in requests were for "selected documents."
Turns out there was at least one page the relative was not sent. In this case, the missing document was not a "huge" discovery, but sometimes it can be.