"Not every valid council in the history of the Church has been a fruitful one; in the last analysis, may of them have been a waste of time. Despite all the good to be found in the texts it produced, the last word about the historical value of Vatican Council II has yet to be spoken."
Ratzinger, Joseph. Principles of Catholic Theology: building Stones for a Fundamental Theology. San Francisco: Ignatius Press, 1987, p. 378.
Lateran V is an example of a Council which, though valid, was not very fruitful.