Can't keep IndexIX tag in bookmarks lists

Question

For some reason, some of my book files do not seem to have any "knowledge" of the IndexIX paragraph tag, which I need for creating PDF files from a FM book (so it will go in the bookmarks list), and also for when I generate a TOC, because I want to include the index chapter in the TOC.
If I start with a book file that doesn't have the IndexIX tag in either of the bookmark lists (include or don't include tag), I have no idea how to add it. I can't find anything about that in the help files and I spent a lot of time looking.
I found a workaround, which is to copy a book file from some other book that shows the IndexIX tag in the include or don't-include list. I delete all the FM files from the book file, and then I add the files from the current book I'm working on. This book file does reference the IndexIX tag. I rename the book file for the current book title, and I'm set.
However, even that workaround isn't working today. The IndexIX tag is there at first (because it was in the book file that I copied), but after I add some files to the book, it suddenly disappears. I haven't figured out what exactly is causing that. But there must be a normal way to add a paragraph tag to a book file!
OK, here's the part I dread: telling you all which version of FM I have.   It's version 8. I don't have any control over that at the moment (my employer makes that decision), and I really need to fix this problem now, so I hope there's someone here who won't tell me you're not supporting version 8 any more. I know that, but I'm hoping someone reading this will have encountered this problem before and knows what to do.
I'm running FM on a Windows 8 system. I don't think compatibility is an issue, though, because I've had this problem with the IndexIX tag for years. After I used the workaround, I just kept updating the same books, which were derived from the previous versions, all of which had IndexIX. But now I'm creating a new book and the problem has resurfaced.
Thank you!

Answer 1

Hi Arnis,
Thanks for the reply. I don't think I explained my problem very well.
I do know how to create a standard index, how to put markers in the material, and how to use different levels of references. Usually, after I create the index, I then create the TOC. I do it in that order so that the index is listed in the TOC. But for that to happen, I need to include the paragraph tag for the word "Index," which is the title of the index chapter (along with Chap Num, Appendix, and other tags I want in the TOC). The tag for that title is "IndexIX". This works fine in several of the books I manage, but in some cases, I can't seem to keep the IndexIX tag in the list of tags to include in the TOC. At some point, that tag disappears from the list of known tags in the current book. I have no idea why that happens - I haven't removed the index from the book file, so the tag should still be there.
Here's the dialog box I'm referring to. It is posted when I select Add -> Table of Contents from the book file:
In the above example, I had already created an index, and the title (or chapter name), "Index," is tagged as "IndexIX." This tag is in the list of tags to be included in the TOC.
But in some cases - and I can't figure out why - when I create an index in a book in the exact same way that I always do it, that tag doesn't show up in the "Don't Include" list when I create the TOC.
The only workaround I've come up with is to copy a book file from another book in which the IndexIX tag is present and works correctly, delete the files in that book file, and add the files for the current book into the copied book file. The IndexIX tag is still in the list. I can then create a TOC that has the index listed. At least, this has worked in the past. I haven't needed to do this for a few years, but I am now creating a new book that needs an index, and this time, even my workaround doesn't work. Anyway, there ought to be a more straightforward way of getting the index listed in the table of contents.
I hope this makes more sense!
Thanks,
Joyce Wermont