I get this message when I try to install the combo updater for Sierra 10.12.6
macOS Sierra update can’t be installed on this disk. The volume does not meet the requirements for this update
I have. MacBook Pro (13-inch, 2016, Four Thunderbolt 3 Ports)
Memory 8 GB 170 GB of free space
Have tried Safe boot, Zapping the Pram, DiskWarrior
I just wanted to rerun the Combo

Apparently you aren't the only one encountering this issue with the combo updater. You will find some suggestions from Apple in the Apple Support Communities.

Thanks for info. I had already tried a bunch of those ideas including reinstalling from the recovery disk the whole system (not an erase) and no success. I guess I will have to wait for the next update and hope they fix it. I had the same issue much earlier and they fixed it so I will see

Sierra is no longer under development and while their might be a security patch any updatesare highly unlikely. There is however an upgrade, High Sierra (MacOS 10.13.2) which is a free download from the App Store.