It gets better!
First, glad to know I'm not alone on this. Second, here's another endorsement of HUCA.
So I realized after the ticket was reissued that the first leg of my return which had been a DL-codeshare was changed to a KL-coded flight in the agent's attempt to apply the GUC. I called back (now 24 hours after initial issue) and explained to an agent what had happened. Eleven minutes later, she had it all fixed and the GUC applied for the whole return trip back. As she said, lots of people just don't know how to use the Deltamatic system to get the GUCs confirmed. She was aghast when I told her I'd been on the phone for 2+ hours the day prior.
I suppose the moral of the story here is, we must persist in order to get the full value of GUCs!