After performing a significant amount of research and reading posts on other sites, I have concluded that many Windows 7 systems are not displaying Windows Update notifications when updates become available.
The issue occurs when Windows Update is configured to "Check for updates but let me choose whether to download and install them." For those trying to avoid Microsoft marketing "updates" promoting Windows 10, this is the only reasonable option currently available.
Unfortunately, for many systems, Windows Update is no longer alerting the user when updates are available.
How can Windows Update be fixed to show notifications when updates are available?
Note that Windows Update Notifier is a third-party workaround, but I am interested in learning how to fix Windows Update when it displays this symptom.