How to Identify Missing or Incorrect Cross-References in a Manual Index

[bine_ro]

I am currently working on manually indexing over 6,000 entries in a book that contains countless cross-references within the index. Since I'm doing this chronologically and many of the referenced entries don't exist yet, I have to manually type or paste the cross-reference entry. Unfortunately, I’ve noticed that the editor who provided me with the file (a PDF with comments) occasionally made typos or omitted parts of the entry names.

Is there a way to identify cross-references in the index where the corresponding entry doesn't exist?

<Title renamed by MOD>

[Robert at ID-Tasker]

Done. Now it's just a case of what to do with them:

(fixed sorting order)