This one I know for sure. John was English for Johann common in Czech, Prussia, Germany, and Dutch and some other countries nearby. I have mennonite background culture in my tree. The J was pronounced as we would normally pronouce the Y sound --like 'Yohann' My granfather is a Cornelius. So --NO it is not the same! Some Cornelius's were called Del for short or nicknamed Corny. Glad I could answer that one for sure!