Manuscript Preparation, Copyediting, and Proofreading

Q. I understand how in proofreading (as opposed to copyediting) you write only the proofreaders’ marks in the text, with corrections and operations in the margins (such as writing a caret in the text to indicate insertion, but putting the letter to be inserted in the margin, not above the caret), as in figure 2.7 of CMOS 17. But is there some protocol as to which notations go in which margin? Do they all go in the left margin, or do you split them up evenly between left and right?

A. As long as they are readable and in left-to-right order, it doesn’t matter how you divide corrections between the two margins.