I hear improv a lot. Especially when you can't remember how it goes. It is called the Folk Process. You couldn't call it that in Jazz.

Apparently when Seth Lakeman is present in a session you will hear it from every wannabe, but not from him. He could blow them away with a couple of bars, but what would it do for his image? The wannabes are there to prove something to themselves and he gives it to them.

Now that is a professional at work.