No replies to this yet, but I have exciting news! Based on info from an earlier post in which someone noted that a micro-SD card which had been unrecognized on his phone and computer suddenly re-appeared after several hours sitting in the card reader on his computer, I left my card in the SanDisk adapter on my PC and HOPED! After ~1 wk of sitting there unrecognized through many hours of opeation and multiple re-boots for various reasons, the card suddenly appeared in Windows Explorer!! I immediately successfully copied the contents to my hard drive (recovering all the precious pictures I thought were lost!). When the data seemed to continue to be accessible, as opposed to the earlier report (which said that the card quickly became unrecognizable again), I re-installed the card in my phone - and it has behaved correctly since. I plan to buy another card for the phone and use this one for long-term storage, but I’ve learned how important it is to maintain a current backup (cloud or another medium) for the removable as well as the internal storage on my phone!
I don’t have a clue about the mechanism for this miracle micro-SD recovery, but I hope somebody else might benefit from my experience.