I'm not sure what happened, but now I have directories:
and much of what I'm looking for is in folder (files) in the non-"-1" directory, and now inaccessible in Thunderbird.
Ideally, I'd like to be able to merge the now-inaccessible items into the (same named) folder(s) "-1" directory. Even a reliable way to simply rename (copy or move) the files to give them different names, if I could then reliably use Thunderbird to move the items around and manage the folders the usual way from them.
I'm a little gun-shy about messing with T'bird's files "manually", since it sometimes seems to take extreme offense, and there's important stuff in there.