I don't know that it is even possible to know that and therefore would have no practical applcations.
Exactly. My sisters and my wife were exposed to my mother at the same time, my wife and one sister caught it but my other sister didn’t. Negative for antibodies, never had it, consistent negative PCRs.
The point is that even if you were indeed exposed to someone shedding virus there is zero indication that you are now “immune”.