It is often said that one troubleshooting attempt for macOS is
On a machine running macOS 10.12.6 an attempt to do so will result in the ominous error message from Installer.app:
macOS Sierra update can't be installed on this disk.This volume does not meet the requirements for this update.
Similar to the error message here on Ask Different: macOS Sierra update can't be installed on this disk.This volume does not meet the requirements for this update
Without giving away the slightest hint at what the requirements really are.
After searching the net it appears in this case to be caused by later SecurityUpdates installed that increment the build number:
If you previously installed Security Update 2017-001; then that's expected, at the moment. The installer script checks for a build version of 16G29 or older; but after 2017-001, you'll be on 16G1036.
Perhaps Apple will eventually refresh the combo package to reflect recent changes.
Apple Communities: 10.12.6 Combo Update, Nov 7, 2017 10:38 AM
The machine in question runs 10.12.6 (16G1408) and had the SecurityUpdate 2018-003 applied. A freshly downloaded ComboUpdate from Apple: Download macOS Sierra 10.12.6 Combo Update Date: Post Date: Jul 19, 2017 reveals an installer package that is dated to 15. July 2017 at 10:19. So, no updated ComboUpdater as hopefully hinted at in the community answer at Apple.
How to fix this situation?
Preliminary ideas: Rolling back a security update seems not really possible. Would just changing the build number of the installed system and then re-applying Combo and Security update solve this impasse?