It’s a tricky question.
Anything the Church declares to be infallible must be something already contained within the original deposit of faith known to the original Apostles (presumably there was an original apostle who witnessed the Assumption of Mary into heaven).
On the other hand, there will always be new issues that arise, where someone will ask, “Ah, but when the original apostles said X, did they really mean that what we now know about Y was also true?” Thus, there will always be a need to ask questions about what the deposit of faith really means.
Also, one should always remember that words and language are imperfect symbols for the objective truth, and that sometimes it’s difficult to read into ancient writings and know exactly what message the author intended to convey. But the spirit of faith still lives with the Church to interpret the same old deposit of faith, but in new ways to address new problems and issues.
Most of the time it’s a matter of negative theology, where the Church says, “No, A, B, & C are definitely not consistent with the deposit of faith.” But every now and then, there does arise the need for statements of positive theology, such as with the doctrines of papal infallibility or the assumption of Mary. The original apostles of the Church would have known these things, but they did not write them down explicitly at the time… or if they did, those writings did not survive the ravages of time.