Discovered 5 days before its closest approach.
It’s amazing how much “stuff” is out there to learn, and how something can sneak in so “close”.
But the other part that I think the original OP is sort of amazed at is that we're unable to detect these through some sort of automated system more accurately. It isn't fair to compare our space/vision capabilities to the eyesight of a person alone. Do we not have satellites or installations doing ""short range"" scanning with radio/laser/something-else-I-am-not-an-astronomer-don't-hate-me ? How come it was an amateur picking this up so close to the specific date?
R-squared is not your friend. This would take a massive amount of energy.