Oh, well ... so much for my initial enthusiasm. I was too eager to wait for Australia to wake up, so I ran the update after all. I ran only KB2919355, because the other two that are showing (KB2990967 and KB3013769) both depend on it.
Alas, same behavior as so many times before - update installs, computer starts to boot into Windows, then just before fully booting, says "We couldn't install the updates" and then backs the whole thing out. Once rebooted, all update history is gone, though you can still see Installed Updates.
Error code this time: 0x800F0922. I've seen this one before, though not recently.
Ran "SFC /SCANNOW" again - ran it many times today between attempting to fix other possibly related problems - scan is still clean. New CBS.txt link is here:
https://www.dropbox.com/s/w4g42vbk4kdvpcq/CBS_HappyTSW_150427-2.txt. (Sorry, it's big - contains all of today's scans.)
[One interesting thing though - which may be due to your fixes, or possibly to some other fix attempts I ran - the Windows 8 "camera" app can now access my webcam and make videos. For months, since an earlier round of Windows Updates and other software updates, none of the apps (Camera, Skype, GraphStudio, or the software that came with the webcam - WebCam Companion 4.5) have been able to access the webcam's imaging device, though Device Manager claims it's working fine, and its built-in microphone works fine with all apps, as do the buttons on the camera - it is only the video portion of the device that doesn't work. (Camera is fine - I have two of them - both work fine on my other (Win 7) computer and exhibit the exact same dysfunction on this one.) Since running your latest fix, the Camera app now works - I can take video and still shots, which I never could do before - though the other three camera apps still cannot access the webcam's image device. I mention this here because it seems to be related - the camera failed about the same time as the failed Windows Update, I think - the word "camera" appears a bunch in the corrupted files you fixed for me - and your fix appears to have partially fixed my webcam problem.]
Anyway ... now what?! You have already helped me get past a step that nothing else has fixed - the clean sfc scan. But still no joy on the updates.
So I eagerly await your next brilliant move! Thank you so much for your help so far.