I've only glossed through, so hope it's not been covered.
About 1970, I was working for what E Gann would have called a steam-ship company's airline. All our licenses had to be double checked cos we were in trouble and were being checked down the route every few days.
A flight engineer had never had a license, and had been flying for years. It seems he was good at his job, and well liked. He got caught on a routine check at some distant destination.
Don't know what happened to him - apart from a lifestyle change.