Interesting. I earned 4 Q3FNs. I used them for 3 different reservations. When I made the second reservation, I asked the DD to use the one that would expire the soonest (I made the same request when I made the first res). She was able to see I had already used the oldest one. When I used my last 2, the agent was able to see which 2 were already used.
I also kept track of my certs too which was good because the agent wasn't able to locate my 4th Q3FN initially.