Citation, Documentation of Sources

Q. I am editing a book, converting it from APA to Chicago. The publisher/​author has made the choice to not include a bibliography. My question is how to write the note when there are more than four authors. Should each author be cited, or only the first plus “et al.”?

A. Follow the rule for bibliographies and list up to six authors; if more than six, list the first three, followed by “et al.” In subsequent notes to the same source, use a shortened form (in which only the first author is listed, followed by “et al.”). Repeat the full form of the note for the first citation in each chapter. See also CMOS 13.78.

[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]