How to Make Newly Added Topics Appear in Index After Regenerating in InDesign

I have a list of Topics for the Index. I'm updating a book from a couple years ago with additional content. This includes new mentions of exisisting topics, but I've also added a couple more Topics to the Topic list. When generating the Index, whether replacing the existing Index or adding a brand new Index from scatch; the page numbers of existing references update, but no new references are added.

For instance, "Term A" is a Topic previously referenced and listed in the Index. Previously, it was only mentioned on page 280. That original mention is now on page 288 as new content pushed it down a few pages. The change from 280 to 288 DOES update in the Index after regenerating; but there are two completely new references to that same term on different pages that were not present before are not showing in the Index after regenerating. 

Similarly, "Term Z" was only now added to the Topic list. It is not showing at all after generating the Index. I have literally copied and pasted the term exactly as is from the Index list to the content to ensure it's not a weird typing mismatch.

Both examples are the case for mutliple topics. 

So it's like InDesign is only checking for the old term references; and nothing new. Is there a way to force the Topic list to recheck all topic references without rebuilding the entire list? I've tried saving and re-opening; no difference. 

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