When you make a change like this and it doesn't show up, one of the first things to check is if the data is cached. Do a web search for "clear frontpage cache" and you'll find some pages with advice.
Be aware, FrontPage is a wysiwig app, and editing FrontPage files by hand is notoriously problematic. Depending on how big the site is, you might consider using FrontPage (if you have access to it) or if the edits are extensive, redoing the site with technology you're familiar with.
Last time I looked at Front Page was before they introduced "extensions". All MS generated code is pretty difficult to decipher. However, taking iframes as a parallel I find that refreshing a page does not necessarily refresh iframes and I suspect that the includes might be behaving in the same way (assuming no errors in your hand coding).