Depends what kind of file you installed from on your Mac. If it is an "Install macOS High Sierra.pkg" file in your Applications directory then UniBeast would use it to create an installer.
Usually System Update would download these intermediary point releases rather than a full installer package, update your Mac then delete the files.
If your real Mac is
still on 17G66 then System Update will be telling you about the newer Security Updates for sure.
Perhaps you could download the latest High Sierra release and make a new installer?
Otherwise as
@P1LGRIM suggested, Search is your friend.
Here's just one example result:
Hi, after using ML 10.8.5 for years, I added a new HD and installed High Sierra 10.13.6 After installing, booting from USB, using Multibeast - when I boot from the HD installation I get to clover and then stuck at apple logo. I've looked at various forums but can't find anything relevant...
www.tonymacx86.com