Well, see I do save a back-up each time I save my work file. Problem is, when I overwrote the 68-page doc, three chapters, I never noticed. Consequently, I then overwrote the copy when I "backed-up" the overwrite.
I've accepted it's a loss and I'll have to print the PDF and recreate the Quark file with that as the guide. Opening in Illy won't cut it, because I need to hasve a Quark file for my client.
Oh, well, every few years I seem to have a sitch like this crop up. Last time was in about 2001 or 2002. I was still working laying out science journals articles in PageMaker 6.5. As I did the layout of an issue-long article, the file was getting hinky with each new save--again, the copy, too. Finally, I got an "end-of-file" error. And I had to redo the puppy.