"The disparity between real-world factory output and Musk’s goals likely means that many of the nearly four hundred thousand people who have already put down a thousand dollars to reserve a Tesla Model 3, which Tesla says will cost about thirty-five thousand dollars, will have to wait until 2019 or later for their cars. "

Extrapolating from the Model S and X to the 3 is probably a mistake. This will probably be true of those at the tail end of the reservation list, but I have a feeling the majority will see their car in 2018. And, of course some reservation holders will not actually buy the car, trimming the list.