As a "young historian" (having graduated this year), my teacher always told me that documents we're using (texts, pictures, etc.) are considered to be ancient (or outdated) quite fast, ten to twelve years old being the maximum to be considered "fresh".
History is constantly working on being "up-to date" with more modern sources or new approaches. I guess the case of Gnl Longstreet was studied by many since 1982, that's why I considered Hite's thesis to be relatively ancient (no offense !). Imagine almost forty years without any book about Gnl Longstreet ...
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Again, this is what I learned during those five previous years, when studying at university, from 2016 to present. By no means I'm considering this "time conception" is universally true.