Karl, thank you for explanation, it does make sense. This inspired me to take a look at log files and I created simple lua script which parses log file and prints generated .4ht files:
Neat, thanks. It now occurs to me that we should be able to use --recorder to determine all the output files on a given run ... once one knows which files are the sources to be run. When I started, I didn't know that. I think it's mostly (though not completely) settled now. karl