I have good news to report - KB2919355 is finally installed. The Win 8.1 x64 install DVDs arrived with a valid Win 8.1 product key. Although Microsoft appears to have wanted me to do an install of Windows 8.1 (that would have required application re-installs), I did an in-place repair that took about 1.5 hours and did not affect applications, data and user accounts. I did an sfc /scannow and a dism /scanhealth - no issues found.
Initially, Windows Update did not show anything but a Check for Updates showed 47 important updates totaling over 800MB. KB2919355 did not appear to be part of the list and there were a number of updates of the 'without KB2919355' variety. I was advised by the Microsoft Global Escalation Team to just go ahead and let Windows Update run but decided to install KB2919442 (pre-req for KB2919355) and then do a standalone install of the KB2919355 components (I downloaded a fresh version but nothing had changed since my earlier download on May 14). All KB2919355 updates installed clean and survived the reboots. All the six updates that are part of the KB2919355 standalone install package show up in the 'Update History' but only KB2919355 and KB295997 show up in the 'Installed Updates'.
I had a brief scare when I tried to login to my standard account and ended up in a 'Welcome' screen loop and had to do a forced shutdown - seems to have been a one-time occurrence. An additional 29 updates have been installed and so far everything looks good (cross my fingers).