Citation, Documentation of Sources

Q. My library shelves are full. I need to make some difficult decisions to make space for new arrivals. Is there any reason to keep my CMOS 14th and 15th editions?

A. What a question. If you had more children, would you give away your firstborn? Find a board and build another shelf.

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