Thanks to both @jitterjames and @nime5ter.
I am baffled: the problem seems quite inconsistent.
I always am logged in with an Admin account and UAC is off. I have had the VoxCommando overlay "on" since I installed the program because it is helpful to know when VC is listening.
This morning, I ran VoxCommando "as administrator" and was successful in using Word 2016 while using the Left Control key to toggle Vox.On and Vox.Standby. Consistently I could see the VC overlay turn green when pressing LCtrl. That's great!
Weird thing was, I then closed and restarted VoxCommando normally (*not* as an administrator) and it still worked with the Word 2016 document. I have no idea why this didn't work yesterday.
However, continuing with VoxCommando in non-administrator mode, when I tried using LCtrl in Notepad++, pressing LCtrl did *not* change the VC overlay and voice commands were not recognized (of course, since VC wasn't listening). If I immediately switched to Word 2016 and pressed LCtrl, the VC overlay turned green and voice commands were registered. If I immediately switched back to Notepad++, LCtrl would no longer work. Very strange.
So, I restarted VoxCommando as an admin. Now the LCtrl was registered in Notepad++ and Word! So, I exited VoxCommando and restarted it in non-administrator mode: Now LCtrl was not registered in Notepad++ nor was it registered in Word 2016!
I don't understand the inconsistency, but, I guess I know to run VoxCommando as administrator to get the best results.
Yes, the fact that the LCtrl key is held down during keyboard emulation is something I have to be aware of and have tried to work around. I wish that were the problem, but I have ensured that is not the cause of the difficulties.
I am using EventGhost at the same time, but not to capture the LCtrl key, so I don't think that is it. Plus, LCtrl works as expected when running VoxCommando as an administrator, so seems like that wouldn't solve the problem if EventGhost were somehow interfering with the LCtrl behavior.
I'll keep looking for a pattern and see if I can figure out what changes the effectiveness of the LCtrl.
I'd also like to find a way to get EventGhost and/or VoxCommando to cause the system to release the LCtrl key press before executing the subsequent commands. EventGhost has the EmulateKeys command that is supposed to do a "key up" only, but that does not effectively cause the LCtrl not to be recognized in Word 2016 (I haven't tried with other apps, but I anticipate it would be the same). That would help with having to be sure keyboard events are not muddled by the LCtrl key.
Anyway, thanks for all the help and testing and suggestions. For now, it seems like the best solution is running VoxCommando as administrator. Will update here if I discover anything potentially useful.