After weeks of frustration and working my way through dozens of articles and instructions from well-meaning friends, I finally hit on a solution that resolved my problem. On the one hand I'm extremely relieved this ordeal is over; on the other I am beyond angry at how difficult this process was for someone with only basic consumer knowledge. People with far more in-depth understanding of computers were offering up wildly different and conflicting advice, none of which worked, or advising that my only recourse was a clean install.
In other words, everybody was just as confused as I was, no matter how knowledgeable. That alone paints a damning picture of this install debacle.
Given how many different things I tried, with command line this and command line that, it's hard to say whether it was the combination of all those actions or whether the last solution was effective on its own. Either way, I followed steps to clean out my Software Distribution folder and that cleared up my issue trying to install KB2919355:
http://www.thewindowsclub.com/your-windows-8-1-install-couldnt-be-completed
To all the rest of you still struggling, God help you, because Microsoft won't.