Where was Catholic doctrine defined before the Catechism? Apparently the Catechism of the Catholic Church (CCC) has only existed since 1992.

Was Catholic doctrine clearly defined in a specific set of sources before CCC? What would a priest have referred to in earlier times, if he had needed to check the stance of the Church on a specific detail?

Is it possible/practical/easy to find out what Catholic Church taught of a specific subject at a specific time in history?
First, the history of the catechism is substantially longer than just 19 years! The catholic catechism dates for hundreds of years - one of the earlier "official" ones was promulgated in 1566.

Catechizing has been a long-standing practice (arguably, God told the Israelites to do that when He told them to write His law on the door posts and tell it to their children).