Q. Have we abandoned altogether the rule to put note reference numbers (and only one per sentence, please) at the end of the sentence? I’ve prepared indexes for a number of academic monographs lately where note reference numbers are sprinkled willy-nilly throughout the text.
A. CMOS does still say that a note reference number1 is best placed at the end of a sentence or clause,2 but there isn’t any limitation—technical or otherwise3—that might prevent authors from placing such a reference4 elsewhere, or that might bar authors from using more than one in a sentence.5
So if a publisher or editor has failed to enforce the spirit of CMOS6 relative to note reference numbers—and the book’s already at the indexing stage7—there’s not much we can do to help you.8
__________
1. Or symbol—*, †, ‡, etc.
2. See CMOS 14.26.
3. A note reference number can literally appear anywhere in a document.
4. Like this one.
5. This sentence has five.
6. See note 2 above.
7. As described in CMOS 16.108.
8. Other than show with this answer how distracting such notes can be. :-)