Word 2000 (9.0.6926 SP3)

I highlight 4 words in a document and press the Style dropdown. I select
'Heading 3'. The text is changed to bold 11 points and that is correct for
'Heading 3'.

However, when I put the cursor on any of the 4 words 'Heading 3' does not
appear in the Style dropdown box. The text is not recognized as 'Heading 3'
when I create a table of contents in which I have defined the toc to include
'Heading 3'.

I have been editing and applying styles in this document for over 1 year.
Many other text sections are set to 'Heading 3' and they seem fine. This is
a large document.

Any help would be appreciated.

Thanks,
Wayne