Careful.
The question of whether this was understood at the time of the Apostles is a little different from whether or not it was dogmatically defined at that time. The writings of the early fathers were in fact taken into account when this dogma was defined.
Defining, explaining and deepening the faith is not inconsistent with preserving the deposit of faith. That is why there have been so called "Doctors of the Church" down through the centuries; Ambrose, Jerome, Augustine, Athanasius, Aquinas etc. They invented nothing new but their theological insights helped to deepen the faith and explain it in new and unique ways.
The faith is a living thing and insights can and do emerge over time.
I’m careful.
“It will be readily understood that in some circumstances, when the question is put explicitly for the first time, the faithful have hesitated. It is even natural that the theologians should show more hesitation than the other faithful. More aware of the apparent opposition between the new opinion and the ancient truth, they may legitimately resist, while awaiting fuller light, what may seem to them unreflecting haste or unenlightened piety.”
This is the seed argument...it was there as a seed, unseen or barely noticed, but grew into a tree that made it so obvious it became dogma - “an extraordinary infallible statement published by a pope or an ecumenical council concerning a matter of faith or morals, the belief in which the Catholic Church requires of all Christians” (Wiki)
According to Catholic teaching, I’m required, if Christian, to accept something that was not taught by the Apostles. “Anyone who runs ahead and does not continue in the teaching of Christ does not have God” - so, how far ahead do you have to get before you cease to be a true church?