What is meant when we say we expect to see a black hole, or event horizon, forming? If we mean that we can no longer detect any signal from particular region, t

What is meant when we say we expect to see a black hole, or event horizon, forming? If we mean that we can no longer detect any signal from particular region, then to that extent, we can assert that what we call as a black hole exists there. We're defining it by its negatives, but I can't see how one can say that even those negatives don't exist. Also its gravitational effects can be detected, so that is another reason why merely claiming a black hole doesn't exist, or never forms, seems to rather miss the mark.