Unless their estimations are wrong
Up until the earth is outside that zone and the chance drops to zero. So expect the "percentage chance" to keep rising until they have enough to data to rule it out entirely.
Why can't astronomy be a more exact science? Well, how much are you willing to contribute to launching more space telescopes for this? And is the budget for NASA currently increasing or not? ( https://news.ycombinator.com/item?id=43090862 )