My mom never had an outbreak of the chicken pox even though she was exposed to it many times. It has always been troublesome for her to fill out medical forms, because there was no known date to fill in for when she had the chicken pox. She eventually did get tested by her physician for chicken pox antibodies and she did have them. I suggested she should put down the date she was tested.
When I was an infant, I was exposed to chicken pox at the church nursury. My mother says I had just one pock on my entire body. Later, when I was twelve and my brother was ten, my brother came down with a very heavy case of chicken pox after being exposed to the sons of my parents' friends. About a week later I came down with a case of chicken pox too, but my case was much lighter than brother's. I'm pretty certain I had a partial immunity.
My dr. told me that if you get the test for the antobodies and it shows you have them, then you don't have to get the vaccine. But then again, someone has to pay for the test.