That really depends on the domain. In fields like manufacturing, resources extraction, and pharmaceuticals most of the valuable information is locked behind corporate firewalls.
Why do you think that? I collect books, mainly published from 1850s to 1980s, and it's not uncommon that they only occur in library listings and sometimes Goodreads when I search for information about their authors and history. This holds for some english language literature as well, but more so for books in other languages.
The Internet is basically a young, small portion of writings in english, as far as I can tell.
