I gave the upgrade install of Windows 10 Spring Creators Update R.T.M. a second try on this pc and it worked.
The only thing I changed before-hand this time around was.:
A. I didn't uninstall Bitdefender Total Security 2018 this time around.
B: I didn't run Bitdefender's Uninstall Utility this time around.
C: All I did was temporarily turn off Bitdefender's Ransomeware Protection @pre-startup and re-enabled it after the install.
This leads me to think that Windows Defender played a role in my first failed upgrade.
Windows 10 Pro S.C.U. x64 R.T.M. install proof below.
P.S. A few good things are fixed.
1: My GOG, Origin & Steam games all on my 2nd ssd survived this time.
2: Huge overdue Microsoft fix- Disk Defragmenter no longer lists the Recovery Partition in it anymore.
The rest of the other changes, I'll slowly checkout.
I've got a busy few day's coming up, so I won't have much time for my p.c.'s.