Of course, it is absurd to use the “words of one who subsequently became pope”. But some people sloppily do this as well. Before he was no pope, obviously none of his words can be papal. But people still cite the “early so-and-so” as though we should read that text because of its authority. Rather, if anything is good in the text, keep it; if anything is unworthy, reject it.
For instance, people will refer to Love and Responsibility by Karol Wojtyla, the later Pope St. John Paul II. Or, people will refer to Introduction to Christianity by Josef Ratzinger, the later Benedict XVI.
But these works should be judged for their theological merits or demerits. They must not be confused with Magisterial teachings.
In practice, it is good to say, “Karol Wojtyla” or “Joseph Ratzinger,” etc., instead of “Pope John Paul II” when referring to these texts.