Welcome to the Forums Mick, and thank you for the question.
Before we go any further, its important to understand a few terms. “Teachings” is a pretty generic descriptor, and it is important to distinguish between a few key words. “Doctrine” refers to the teachings that were handed to the Apostles by Christ-doctrine can not and has never changed. Doctrine is often within the context of Sacred Tradition (capital “T” tradition), which is the faith as it has been taught since the time of the original twelve apostles.
Be careful not to confuse Sacred Tradition with just plain tradition (lowercase “t”) which is merely a historical custom, and not official doctrine. In line with this, you will find “discipline” which is an official practice of the Church (or parts of the Church). Discipline, can and often does change to suit the historical and cultural needs of the Church and any given point in history.
Disciplines and traditions have changed over the course of 2 millenia, but the Doctrine’s and Sacred Tradition of the Catholic Church have remained unchanged for 2000 years. Whenever a source claims to point out the “changes in Catholic Doctrine” it is very important to recognize whether or not it is even a Doctrine to begin with.
“Dogma” refers to a