> Consider: the Library of Congress has (literally) a copy of every work that has ever been in print in the U.S.

This is not true. The Library of Congress has a copy of works that have been registered for copyright with them. I am sure millions of works are created in the US every year that never get registered with the Library of Congress.

While a registration with the LOC isn't a bad idea, in the USA at least authors of written works automatically have copyright of their work, regardless of whether they have registered it for copyright with the LOC.