i just went though this as well. My wife's key was the first one closest to the car. When I got in the car on the drivers side it still recognized her key. I had to plug mine into the key slot to get it to my preferences. Additionally, I wanted to charge her key and stuck it into the key slot after the car was started and it took her preferences. I think that that key closest to the Key slot is the primary. So I just stuck mine back into to slot. All good after that.
Just my experience.