There are numerous distinction fails developing rapidly here.
One involves certitude, and its degrees.
Another involves the practical order.
The Church does not judge internal things, at least not directly.
Going by what is known, we can know at least to moral certainty whether we can or cannot, should or should not, for example, consider someone lost.
You can see an example of this, for example, when S. Robert Bellarmine speaks of someone, in this instance a pope, being rightly condemned as a heretic when it was later determined that this pope was not actually a heretic.
You can see this kind of thinking somewhat paralleled in criminal convictions, at least in principle, where the case and evidence presented rightly leads to a conviction of someone who is innocent.
It would be wrong to not convict in that case.
There are other distinctions, but there is a reason why there are such things as theologians, philosophers, and books.
If you think about it, how else could things work? We can see the alternatives doing much damage to people's ability to see the visible Church for one.