Finally, you can see the finish line. You’ve spent months if not years writing your book, sent it through multiple rounds of editing, from the developmental to copyediting, and now it’s in the final stage of proofreading before being sent to the printer. All that’s left is to review the proofs and append that index. No sweat. You know what you wrote, how hard can it be to run a quick search in Word for the key ideas and alphabetize them? Heck, even a grad student can do it!
You could do that, but both you and your publisher are likely to be unhappy with the end result.