The system is working now by restoring an old registry from December 2017. This resolved the update issues. The step I used were
Enable Volume Shadow Copy to enable copying of files from c:\windows\system32\config\regback which are locked
Copy the SOFTWARE hive (file) to somewhere convenient
Rename SOFTWARE to TESTOLD
Import TESTOLD hive into HLKM using regedit
Examine HLKM\TESTOLD\Microsoft\Windows\CurrentVersion\Component Based Servicing\Packages to make sure it has lots and lots of packages installed indicating it is healthy
Now we have decided to proceed, Remove the HLKM\TESTOLD tree from the registry
Using https://www.tweaking.com/content/page/registry_backup.html Backup the existing registry twice
Modify one of the registry backups by replacing its backed up hives with all of the files from c:\windows\system32\config\regback
Restore the modified backups back to the registry, so now the registry contains the older registry hives, particularly SOFTWARE and Reboot
Windows update downloads and installs a lot of updates for 1703 and reboots
Windows update downloads more updates for 1703 and attempts the Feature update to 1803 and reboots
Windows update downloads more updates for 1703 and attempts the Feature update to 1803 and reboots
Windows update downloads more updates for 1703 and installs the Feature update to 1803 and reboots
Windows update downloads more updates for 1803
Turn on System Protection of the Disk Drive as it was turned off. Make sure that Restore Points can be written.
Clean up downloaded WSU updates, copies of the Windows ISO, copies of log files no longer needed etc
The only issue left is that the registry has the non-Microsoft programs with versions installed as of December 2017 but the disk has non-Microsoft programs are actually installed on disk as of September 2018. So to remove a program the uninstall will fail and we need to use the Program Install and Uninstall troubleshooter https://support.microsoft.com/en-au...lock-programs-from-being-installed-or-removed. There may be issues updating programs, haven't got that yet.
