Hi guys,
here's the thing.
The first thing you have to do is to update RecoveryHD before security updates.
Execute update script from terminal. Then apply security updates as well.
Don't bother modifying distribution (or script) file to install, just use "softwareupdate" command.
1.Download Security Update 2019-004
2.mount dmg and expand pkg
#to open terminal, just right-click the volume - go to Services - New Terminal at Folder
$ pkgutil --expand SecUpd2019-004HighSierra.pkg ~/Desktop/expanded
3.run replaceRecovery script
$ export PACKAGE_PATH=~/Desktop/expanded/EmbeddedOSFirmware.pkg/RecoveryHDMeta.dmg
$ cd ~/Desktop/expanded/SecUpd2019-004HighSierra.RecoveryHDUpdate.pkg/Scripts
$ ./replaceRecovery / /
4.apply other security updates
$ softwareupdate -i -a
5.after reboot, re-install patches. (and clear NVRAM if needed)
This method always works for me.(iMac9,1 , HFS+)