Bill, no worries - read through the thing again, and it does indeed say that the end result will be displayed on the LCD, so my own fault for being dumb.
Anyways, got it going, but still no luck. The guesser goes through the eight attempts, but none of them did the job. Best I got was the first attempt (which is the default), which at least left the LCD on, but just gave me the same 16x2 array of blocked out characters.
One thing though, when I tried ohming out everything, to see if I mucked up my soldering I did notice that I was getting a reading on all pins, as if everything were through a 10k resistor. So unless this is common practice for these boards, I've either got a faulty one or a short in my soldering (which would surprise me, since while my coding skills are beginner, I'm competent enough with a soldering iron…)