Tello EDU swarm, what determines the index number?

[cobATcob.dronz]

I have 4 tellos in a Swift swarm, just starting out but confused on how the AP determines the index number [n] to identify the individual swarm. I assumed that it was the order in which they were connected to the AP, but they are behaving so erratically now I'm not sure. When I restarted [0] because it went astray it started copying [3] instead of running it's own route. And from there it was chaos I think the batteries were getting low. So does the order the drones are turned on after they are all connected to the AP determine the index of the drone? Thanks ,cob