Well, the problem is solved. And the solution's embarrassing, to say the very least.
Following MikeR's advice, I did open a support ticket with MM yesterday. Nick M. replied, asking for an SPX file but first mentioning that whereas in my product field I'd selected v 2014.5, I was licensed for v 25. A search for "Finale 25" revealed nothing more than a PDF ReadMe file but convinced me I'd better look in my apps folder, where I found v 2012, v 2014, and of course v 2014.5—and something with a redundant and far-less-than-forthcoming title: "Finale app." (Its icon, now in the dock, is less redundant but no more informative in a mouseover, yielding the single word "Finale.") Yup: a Get Info check of the icon in the apps folder showed that it was indeed v 220.127.116.11. And yes, once I opened it and then opened the file that had been behaving so bizarrely in v 2014.5, a very quick check showed that some—probably all—of those problems had gone away.
Guess I'm ready to be carted off to the funny farm. My only excuses are (1) that the app. is so determined to hide its version title and (2) that I'm an occasional user who does only 3–4 vocal charts a year.
By the way, any reason not to throw out vv 2012, 2014, and 2014.5?
Thanks, MikeR, Motet, and Buon Tempi, for trying to help this longtime Finale user (who apparently needs help not just with Finale)!