The book of life is a record of all the righteous of every age, their names appeared in the book before creation began (predestination). In this present age of the church, the names of the dead in Christ and those living in Christ were in the book of life before they were born. The names of all the wicked never have or will ever appear in the book of life.
The meaning of names not written in the book of life from the creation of the world” refers to the wicked. Before creation the names of the righteous were written in the book of life, at the creation of the world the names of the wicked were left out of the book.
At the great white judgment of the wicked when the book of life is opened they will realize their names are not in the book and be cast into the lake of fire. The dead will be judged according to their works or what that had done as recorded in the books. One book of life, many books recorded their works.