Thanks for reply. yes, seems so, but in process it may have overwritten the database.
Using the program "everything" to search for all locations joplin appears on my HDs, I'm unable to locate any .md files.
...a bit later ...I had already tried using "normal" version of Joplin, to no avail.
Just now, tried AGAIN. All files back. So weird. And to emphasize, I did try opening the usual version yesterday. So all is good, apart from wondering "what just happened?"
And thanks for drawing my attention to exporting as JEX. Done immediately, to 2 separate locations.