Aha! After all the replies both here and also here:
https://forum.dxo.com/t/how-do-i-protect-or-erase-an-area-when-using-a-control-line/31382/20
…I now understand what to do, and how to achieve it. Sorry for being so slow.
Thanks to all of you.
…and as I posted in the other thread, now that I’ve got 5 VC images in PhotoLab, is there any way to add a description for each of them, that might show up as I “hover” over that small image, to remind me what I had done for each VC ?