I can see all the applied tags in (to only name a few of the programs I checked) Windows Explorer, FastStone, XnView, etc.
Every tag in my entire photo collection has been applied with digiKam.
I have noticed that, although not all of the problem images, but the majority of them, were images taken in 2017.
What blows my mind is that I completely purged my system of digiKam, as if it had never existed; then, I installed it anew and folder-by-folder reinstated my collection and the problem is right there as if I hadn’t done a thing.
Right up until I first noticed the problem, there was no problem.
I think I have a recent version of Exiftool in my “things to install someday” folder; maybe I will get it installed and see if it reveals anything.
Thanks for the suggestions.
I hate to admit it; but, I investigated Lightroom to see if it would be a viable and hopefully working solution to my situation; however, working correctly or not, Lightrooms tagging and tag-searching abilities fail miserably when compared to even a crippled digiKam.