As often happens when one asks a seemingly hard question, the answer is stupidly obvious. I had created a couple of other folders in SAMPLES some time back, and the files I couldn't find were in them.
Thanks for the kind responses, and I apologize for asking one of the rare dumb questions.
Thanks, Lawrie. I just opened NWC and went to File > Open, which took me to the SAMPLES file, which is where the History window tells me my files are stored. The file I was working on yesterday is now listed in SAMPLES, but other files under History that History says should be there don't show up in SAMPLES. So now I have two problems. How did the file I worked on yesterday suddenly show up today in SAMPLES when it didn't yesterday? And where are the others? I opened another file from History, saved it, exited, and reentered NWC to see if it would now show up in SAMPLES. It didn't.
In NWC 1.75c, a help file indicates that the files listed under History are stored in SAMPLES. I have ten arrangements showing up in History, but when I open SAMPLES none of them shows up. I've done searches on my C: drive, and I don't find them that way either. Where are those files stored and how can I find them?
I do have NWC2 and I'm trying to migrate to it, but not being able to find my files doesn't make this easy.
If this is a problem specific to my hard drive, please excuse my obvious ignorance of my hard drive.