Please don't tell me "it's just an estimate"
So, you want no answer then? :-)
The thing is, you cannot prove it's not working by presenting a couple of hand-picked examples. You would need to conduct a fairly large study to show that the estimates are systematically too much off. The fact that the estimate is often within one or two days of the actual end of construction, and in some cases even spot on, suggests that the code usually works pretty well by design or by luck. Your latter example is fairly extreme, but not crazy enough an outlier to suggest to me there really is a bug. It is after all just an estimate, and we know there are often delays.