Steve - N3SL
RESOLVED! After starting "all over" and updating Win10 to the current version and installing microHam from the CD, STILL NO SUCCESS ("cannot create port #x). It turns out (and I'm only presuming this is the issue, as I'm not knowledgable enough to know for sure), the update has resulted in "Intel Active Management Technology - SOL (COM4)", and COM4 happens to be where I start my virtual com port numbers. And it appears (to me) the "SOL" part is very appropriately named!
At any rate, created new ports at COM10+, and the system now works on Win10, v1909.
Thanks to all you replied and offered suggestions. And thanks to W4TV for the latest version info, and AA6YQ for tolerating a non-DXLab issue here! (I really don't know how you do it....)