Link difficulties... fixed
I discovered that in my permalinks of older news items (archives to the left), my navigation menu wasn't showing up. I hadn't really noticed before because I never use the direct permalinks that often.
The fix simply required a tweak in my Blogger archiving settings to use index.PHP instead of index.HTML for the archive name. The navigation menu (and the rest of this site) is generated using a PHP include, and HTML doesn't read PHP.
Turns out I was also able to fix the 4 older posts by editing each one individually, without changing anything in the post, and re-publishing the blog. Blogger automatically changed the permalinks from HTML to PHP files.
Thought I'd share this discovery in case any other Blogger users are having a similar issue.