Сиротских книг больше, чем ожидалось

The body of orphan works—works whose rights holders we cannot locate—is likely to be extremely large, and perhaps the largest body of materials. If the guesses made here are right, 50% of the volumes will be orphan works. This 50% is comprised as follows:  12.6% will come from the years 1923-1963, 13.6% from 1964-1977, and 23.8% from 1978 and years that follow. (The percentage of orphan works relative to all works decreases as time passes; the number of orphan works increases in more recent years because more works are published in later years.) Indeed, if this speculation is right, our incomplete collection today includes more 2.5 million orphan works, of which more than 800,000 are US orphans.

via clir.org

В гигантской библиотеке HathiTrust (более 5 млн оцифрованных книг из американских университетских библиотек), согласно предварительному исследованию, сиротскими являются не менее половины книг.
Думаю, в России ситуация аналогичная.