Didn't the OOD books tell us about this?
Oh wait, the OOD books were about how we could model an aircraft and assume a helicopter was close using inheritance and not about the real world at all.
In the olden days, the flight controllers would write the data on a card and pass it from station to station based on where it was or their best guess if it lost communication. If all else failed, they could grab a pen and make a copy if the plane could be in more than one area.
Modern air traffic control assumes controllers know where everything is all the time. Old air traffic control assumed that the controllers had a good idea but when when things went wrong, all the pilots would continue to a plan and there were ways out when those plans didn't work out even if there was no communication. Oddly enough, one has had far fewer issues than the other with no gains in traffic between the two systems.