Okay,
I think I understand what you are doing, but to be honest, you are doing something far more technical than we've ever been hands-on with before.
As far as we are aware, there is no way to label/mark what recorded footage is from the MicroSD cards and what is from the NAS.
We will edit the title of this thread to something that better explains the question you are asking and hopefully another user here on the forum might have some more experience of this kind of recording setup you have.