Manuscript Preparation, Copyediting, and Proofreading
Q. The 16th edition 13.7, point 4, states that it’s permissible to omit note reference marks from a quotation “unless omission would affect the meaning of the quotation.” Does the same principle apply to author-date citations within quotations? I.e., can author-date citations within a quotation be omitted without introducing an ellipse?
A. Author-date citations should be retained, or (as you suggest) their omission should be indicated with an ellipsis. If this would result in a manuscript full of ellipses, and if the citations are not needed, an alternative is to omit the references and explain your method in a general note.