Well, I have sussed out the issue.
First problem is that the SD card I was using is some how corrupt. I can write files to it and read them as well, but, if I put a simple picture file or something, it belches and the computer gets upset. So, I tried a new SD card.
That's when I figured out the original Pi Zero W was inept. Now, that may well have been my doing not fully understanding the process before I unleashed my ham handed attempt at diagnosing something I knew nothing about. Well, now, at least, I know very little which is more than nothing!
With another Pi Zero W, a different SD card, and the snapshot firmware, it boots, connects, and the pit thermocouple and two probe ports read values reasonably close to room temperature.
This was one of those cases with multiple failures which seem to compound exponentially. I hope this result helps someone in the future.
Thanks for your help Bryan.