I too see some in a folder called "Previous iTunes Libraries" in the sequence of folders you gave in your original post. Mine go back to 2008.
Different versions of iTunes required that the existing iTunes library be "updated" after the new version of iTunes was installed. I suspect these previous are the older versions.
Probably safe to delete since your current iTunes library is backed up 19 different ways, right?
On a Mac since 1984.
Currently: 27" iMacs, Macbook Air, macOS 10.14.x,; iPhones, iPods and iPads galore!