Public revelations cannot contradict. They can always be reconciled, though it may take the Church some time to iron this out. Public revelation is cumulative. Doctrine does not change, but it can be developed. The development is permanent.
Private revelation is tricky. Two private revelations can be approved, in that they are both not incompatible with public revelations, but they are not necessarily compatible with each other. Lucia’s needs in 1917 were different from Bernadette’s needs decades earlier, or Faustina’s a few years later.
You and I might be taking medicines prescribed by the same doctor. That does not necessarily mean it is harmless, let alone healthy, for you to take mine or me to take yours. Private revelation is not cumulative. The council of Nicea, or Forence, is permanent. They will not be undone. Unlike them, Private revelation is not permanent, not cumulative.
This fact was not always presented well, especially about Fatima. Thus, we see people who begin their post with “I know Fatima isn’t public revelation, but…” Then they describe Fatima as if it were public revelation. Over use of private revelation was relatively harmless decades ago, when people had a solid grasp of public revelation. This is not the world we live in today.
Thus, I think from now on the Church will give private revelation much less attention than it had.