Wow, thanks for all the suggestions, and so quickly.  

I work out of my home in Dallas, so I'm likely surrounded by neighbors with Windows computers.   I guess I'll pay one a surprise visit.  Luckily, I live in a friendly neighborhood.

However, I may have really screwed up.  Disk Warrior reported that the Directory was messed up.  I let it "fix" it, and although the disk did mount afterwards, it contained nothing but gibberish... Asian fonts and weird characters, UNIX Executables and aliases to nowhere, with Modified Dates spanning 1996 to 2020.

I notified client, and he disclosed that he's been having problems over there.  He is going to copy the media again onto another disk.  So good news there.  I guess I'm out of the woods for now... at least until I get the next disk.

Thanks again, good people of Ae!