My suspicion is that the U.S. and Afghan government deliberately lied to these people in Afghanistan in the months leading up to the May 1st (then September 11th) departure dates. This would be done to avoid the obvious PR problems Afghanistan would face if large numbers of its residents who had been working with the Americans suddenly started packing up and leaving. The chaos and bedlam we've seen over the last couple of days would have happened months ago.
It's like the obvious signal that goes out to the public when everyone working at your local police precinct calls out sick and is seen driving out of your town in an SUV loaded up with everything they could fit in it.