Should I use square brackets around commentary that was inserted into a quote in Chicago style?

Question

Working with a reissue of a text originally published in the '50s that must now conform to Chicago in the new edition. The author used many excerpts, unfaithfully copied and inconsistently attributed, from other texts. No portion of the book may be rewritten, but punctuation will be changed and long in-line quotes can be changed to block quotation when over 100 words, as per Chicago's general recommendation, and sometimes less.

In the below, he used an excerpt from another work and made two alterations: insertion of the word, "public" (though without brackets to indicate the change), and made a comment within the excerpt, which he inserts in parentheses, and adds an exclamation outside the parentheses. Here it is in bold for illustration; single quotes were in his original:

To quote Knopf and Marks, in those bygone, ‘preindustrial’ days, 'the public building industry, in fact, stood out from the normal activities of more or less independent craftsmen in their little workrooms, as the towers of a cathedral or the battlements of a castle stand out above the houses huddled about their base ... The castle at one period, admittedly a time of exceptional activity, found employment for 500 masons, 40 smiths and carpenters, 200 unskilled workers, and 300 carters (medieval truck drivers)! The meaning of these figures will be understood if it be remembered that the population of London, in 1477, was probably no more than 30,000.'

All of this now converted to Chicago and in block quotation contains, as I see it, the following changes:

1. 'preindustrial' to "preindustrial" (then follows the block quotation)
2. public to [public]
3. (medieval truck drivers)! to [(medieval truck drivers!)].

Is this correct usage of square brackets in the third point; should his parentheses be included in between the square brackets? (Square brackets alone would suggest paraphrasing, which this is not. It's his comment inserted into the text.) It's crucial to preserve his intertextual comment but not confuse the reader as to whose words these are.

Answer 1

I would handle situations #1 and #2 just as you suggest. Your proposed treatment of situation #3, however, strikes me as being less felicitous.

The complication that you face is that, on the one hand, the author has added language to a quotation without asserting ownership of it (in adding "public" to the first sentence of the quotation), while on the other hand, the author has attempted to claim responsibility for another embellishment (in adding "medieval truck drivers" to the second sentence of the quotation) by parking that intrusion (aside from the exclamation point) in parentheses. This puts you in the position of relying on square brackets to indicate two kinds of additions: unacknowledged ones like "public," and acknowledged ones like "medieval truck drivers."

I can see how a desire to distinguish punctiliously between these two categories of interpolation might lead you to try to preserve the author's original parentheses within new square brackets. But most readers, I suspect, would have no idea why you were double-punctuating "[(medieval truck drivers!)]." in that way. Moreover, this proposed treatment doesn't exactly reproduce the author's original interpolation because it positions the exclamation point inside the parentheses (where the author should have put it in the first place) instead of outside the parentheses (where the author actually put it).

You might achieve a more consistent and coherent result by using only square brackets and dispensing altogether with the author's occasional and haphazard efforts to signal such intrusions and asides through the use of parentheses. In situation #3, that would mean recasting the author's original wording as "[medieval truck drivers!]."—with the original parentheses deleted in favor of square brackets that enclose the exclamation point as well as the comment.

If this issue comes up repeatedly in the author's quotations, it might make sense to add a sentence to the introduction to the new edition (if there is one) saying something like "Throughout the book, comments that the author inserts within quotations are indicated by square brackets." Of course, you would then have to scrupulously avoid ever using square brackets in quotations to introduce your own substantive alterations or additions to the text. But given that you are already constrained from altering the language in any meaningful way, that limitation shouldn't pose much of a problem.

Good luck with what sounds like a challenging assignment. The care you have shown in checking the cited quotations against the wording that appears in the original source material speaks well of your thoroughness.