Not your usual lost files problem

I'm using classic 5.7.1, probably for upwards of 15 years at this point. When I started it was explained to me that LR catalog is not the same folder tree as windows, and that I could just thrown everything into one big piles and make a folder tree in LR and let LR sort it out. But I rejected that approach: if lightroom was lost or corrupted I wanted to be able to find the files manually in windows.

No problem for years, decades. Until now.

Inside my custom desktop housing I have a D and a Y drive platter. (C is solid state). I'd been saving every thing onto D; Y was on line in the tree but unused. Recently I got close to maxing out the D drive {2.8 TB) and an evaluation indicated the drive had years of use left. So I cut and pasted folders from D to Y, freeing up space on D.

One of the big problems with my approach is that you have to decide how cross reference folders, so are you going to put all the carnivals in a carnivals folder, or all the carnivals in New York in a folder along with the NY pride marches, and so on.

So now a relatively small number of Y drive folders appear to be correct in the LR folder tree.  The others are names but contain no files. Others have the files but no names appearing in the LR folder tree. Some folders don't appear in D but do in Y. Finally, I have tried to keep clear of "libraries" and look only at

the folders not the libraries.  Most upsettingly, some seemed to have simply vanished.

I have crashplan. I should be able to turn the clock back to where it was before I mucked around with everything. Still, the Y drive has 1.8 TB (only photos 0of space used, the D drive 35.4 GB of photos.

In a word, yikes.