Complex sentence: This theory, elaborated by theologians beginning in the Middle Ages, never entered into the dogmatic definitions of the Magisterium, even if that same Magisterium did at times mention the theory in its ordinary teaching up until the Second Vatican Council.
Split into simpler sentences: This theory, elaborated by theologians beginning in the Middle Ages, never entered into the dogmatic definitions of the Magisterium. Still, that same Magisterium did at times mention the theory in its ordinary teaching up until the Second Vatican Council.