Thanks, Guys:
1. On a whim, I decided to trash the TIME MACHINE "PLIST" from the Preferences Folders in both the OSX Library and my User Library.
2. Re-started the computer.
3. Clicked on Menu Bar icon to do a manual backup.
4. Selected AIRPORT DISK for the backup (i.e. the same procedures used when setting up Time Machine for the first time in October).
5. When b/u done - 40 MB which took less than 2 minutes, so I knew it was not a full b/u - I entered Time Machine . . . and all files and folders from previous b/ups were there (and accessible).
Ditching the PLIST seems to have resolved the matter. Time will tell if the problem rears its ugly head again.
