Thank you JoeP.
Late yesterday I started rebuilding the index and walked away; the rebuild paused every now and then and then restarted and ultimately ran to completion. The process ran for close to an hour; it was not five minutes that I know.
This morning I tried (File Explorer) selecting "This PC" in the left pane and searched for *.doc in the search box. The green bar grew for about 30 seconds (next time I'll use a stop-watch) and reported 23,996 items , including those on SUBSTituted drives V:, W: and so on. A search on drive shows no *.doc, which is how it should be, but still surprised me that I have not yet stored a Word2003 document somewhere there!
Then I ran a check with Everything.exe. The search "ext:doc" returned 16,035 items, or about 2/3 the total from File Explorer, which makes sense to me, because much of my writing (DOCuments) is in web pages (W:) and my bonaVista pages (V:).
The Everything run time is non-existent because Everything searches not the drive, but the index database, in memory, so very fast.
The Explorer run time is especially inflated in my case because, I suspect, File Explorer looks up a table for each reference to a SUBST drive; the fan fired up furiously during the search!
This HP15 laptop has an SSD drive.