As Ackbeet suggested, the word "validity" doesn't work here. Are you asking about the "value" or "meaning" of the "inverse" concept? If so, then there are many different ways in which the word "inverse" is used in calculus. Are you perhaps asking about the "inverse" of a function? Or are you asking about "inverse" operations (in the sense that "integration" is inverse to "differentiation")?
I'm afraid you will have to make your question clearer and more precise before we can give an answer. Perhaps it would help if you told us why you are asking this question.