Manuscript Preparation, Copyediting, and Proofreading

Q. What do you say (or do) to an author who makes extensive revisions (without tracking) to his original manuscript after you have sent him the copyedited version? Just wondering . . .

A. Please use your imagination; we would rather not say.

(As for the manuscript, Microsoft Word’s Compare feature might help.)

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