OK, so I'll answer my own posting. Unfortunately this seems to be the trend on vendor-sponsored forums like this one
The command that I was using was correct. Epic runs as a separate process and when you use the -b option your process does not connect to the console. So it looks like nothing is happening (your startup of epic does not wait for epic to complete). So I had to add the -log logfile switch and wait for the completion of the process and scan the log file. The command ended-up like: epic.exe -b -c "check_completeness" -log
logfile document and then I had to add some trickery to get my invoking batch file to wait for epic.exe to complete. But it does seem to work.