I finally (okay I'm slow but ...) figured out that the only apps which update-menus will find are those which have been installed using *.deb packages system. ('apt-get install' or 'dpkg -i' or however.)
But I have several important (to me) apps which I've accumulated over time in /usr/local/bin or /opt/bin or wherever. Is there any way to get them on my menus? Tia, Maury