Amazon books are downloaded to Kindle for PC, then imported into Calibre, all others downloaded into a folder with others of that source, (feedbooks, Baen, Gutenberg) and then imported into other libraries in Calibre.
When would the ASIN change? The only thing I remember doing was changing the covers and pushing the books out to the Kindle again. Even so, I'm almost positive that I deleted all the books from the collection and added them again. I would have thought that it would be the next best thing to creating a new collection... I'll try it one more time.
OK... I just deleted all the books from the collection and added them again. No difference. I deleted the problem books from the device (without removing them from the collection) and then reimported them from Calibre. Both collections now show all the books. The immediate symptom is solved, but the problem remains unidentified.