Fixed!
To remove the "Group" word from the Title bar I first selected all of the worksheets in one of the problem files. Then I right-clicked and lo and behold, "Ungroup" appeared in the menu. I clicked that and then the word "Group" was removed from the filename in the Title bar.


I have not the foggiest idea how that word appeared, but I must have done something in the last couple of months to make it appear. Anyhow, the file is now "ungrouped" and I am happy-happy.