It bears pointing out that the definitive proclamation of a truth does not mean the truth wasn’t believed before–rather, quite the opposite. Usually, when the whole Church already believes something, there is no need for extraordinary intervention. However, when the Pope or a Council decides a truth has been cast in doubt, they may choose to make a definitive proclamation after listening to the debate.
Similarly, truths can and often are definitively proclaimed in an extraordinary manner multiple times.
Similarly, some truths are definitively proclaimed which are not dogma themselves (truths revealed by God), but rather are logical necessities based on actual dogmas. The Church teaches these secondary truths definitively with infallibility as well.
Then Cardinal Ratzinger explains the nature of the debate of papal infallibility well:
The primacy of the Successor of Peter was always believed as a revealed fact, although until Vatican I the discussion remained open as to whether the conceptual elaboration of what is understood by the terms ‘jurisdiction’ and ‘infallibility’ was to be considered an intrinsic part of revelation or only a logical consequence. On the other hand, although its character as a divinely revealed truth was defined in the First Vatican Council, the doctrine on the infallibility and primacy of jurisdiction of the Roman Pontiff was already recognized as definitive in the period before the council.
On the other hand, as Ratzinger explained in the same document, Pope John Paul II definitively proclaimed that ordination is reserved to men alone, but did not proceed to a dogmatic definition. While we know this doctrine is definitively true and proclaimed infallibly, the debate is still open as to whether this is a truth revealed by God, or a logical consequence of the dogmas relating to the constitution of the Church and the nature of the priesthood.
This whole document is a really good read on the topic of the Magisterium:
ewtn.com/library/CURIA/CDFADTU.HTM