Dei Verbum 8 says:-

The tradition that comes from the apostles makes progress in the Church, with the help of the Holy Spirit. There is a  growth in insight (perceptio) into the realities and words that are being passed on.

This is fine in itself but can be used to support errors. Frank Duff, talking about the ‘True Devotion to our Lady’ makes what is in effect a useful commentary:-

We are tempted to think that because we see a doctrine in fuller detail than the early Christians, we see it better. I do not think that we would be justified in so thinking as a general proposition. The seeing of a doctrine in greater detail may not be a better seeing of it. For instance, does the modern Catholic who views Jesus in the light of all the protective and explanatory definitions of the Church see Him any better than the early Christians saw Him?

The growth in insight seems to be a growth extensive, i.e. we are furnished with a greater number of propositions about say, Christ or the sacraments, which we see to be true. There is no guarantee of a growth intensive, that is into the depth with which the average believer penetrates the mystery in question. In fact, some words of St Thomas suggest that the opposite is rather the case:-

The final consummation of grace was through Christ, and so His time is called ‘the fullness of time’. Amd so those who were closer to Christ, whether before like John the Baptist or after like the apostles, knew the mysteries of grace more fully. Likewise with the state of a man, we see that perfection is in youth, and that a man has the better state, the closer he is to youth, whether before or after (2a 2ae 1, 7 ad 4).

The growth that Dei Verbum speaks of appears thus as a divine compensation for the lessening of insight of which St Thomas speaks.