Exactly. What some people don't realise is that traditional, pre-Reformation Christianity has always provided for the development of theology and doctrine, through the idea that the ordained successors of the Apostles inherit authority from Christ to further interpret scripture and and adapt teaching for the time. Furthermore the traditions of the church, inherited from its earliest beginnings, close to the lifetimes of the Apostles, are thought to be authentic sources of doctrine, alongside scripture itself. So scripture and tradition are two parts of the "deposit of faith".
The sola scriptura Protestants dislike all this, understandably, since it has given rise to abuse over the course of history, and consider it too dangerous. However the potential snag of sola scriptura is an ossified faith, which comes to seem more and more irrelevant to the modern world.
Regarding Purgatory, my understanding this derives from the practice of praying for the souls of the dead, which seems to have taken place right from the beginning of Christianity. Doing so implies that these souls may not yet be in a heavenly state but some sort of intermediate state of purification. The idea of after-death purification is also, I gather, to be found in Judaism. The notion of Purgatory as a place, as opposed to a state, is not actually part of Catholic teaching, just popular representations of this state in art etc.