New index topics are ignored when generating index

[#1]

InDesign v15.1.2 x64 (Windows 10)

We are creating a new edition of a book.

I copied the previous editon's index file, added some new topics in Topic view, and generated an index. None of the 30 new topics were added to the index. Zero.

We have never made the effort to create reference markers in the book's files; the Reference list in the index panel is empty. It nevertheless managed to get the new page numbers correct for the previously existing index entries.

Is there some special option somewhere to have the index generated using additional topics?

[#2]

InDesign v15.1.2 x64 (Windows 10)

We are creating a new edition of a book.

I copied the previous editon's index file, added some new topics in Topic view, and generated an index. None of the 30 new topics were added to the index. Zero.

We have never made the effort to create reference markers in the book's files; the Reference list in the index panel is empty. It nevertheless managed to get the new page numbers correct for the previously existing index entries.

Is there some special option somewhere to have the index generated using additional topics?