Am not a Catholic. So this is only an outsider's comment.
The Church isn't a fossil but a dynamic body animated by the spirit of God. Discernment of the truth evolves over time. It doesn't mean that official teachings can contradict each other even if they come from two distinct eras (although context and language matter), but it does mean that the truth is progressively discerned as the members of the Church as a whole become more spiritually mature and experienced. This will culminate in the eschaton.
You shouldn't be distressed that a 20st century Pope finds a different way to express the truth and divine revelation than a 19th century Pope. Such a thing is allowed. Our perspective, if it is enlightened by the Holy Spirit, is not to be discarded, which is why even the saints disagree on how to express certain things.
Also, it is the job of the bishops to receive and interpret what previous bishops and councils taught. Let them handle it, if you are or are becoming a Catholic. You can always discuss it with your priest anyway, no?