Anyway, until recently, they only had rough predictions on potential shipping times or even less... there were too many uncertainities.
Now they are starting to share more information simply because the number of potential uncertainities are highly decreased, so this date is mch more accurate than any earlier dates... not because those dates were already elapsed, but because we see FCC certification went through, they state components are arrived, etc, so it seems it is up to the factory and logistics which will determine the actual shipping date of the phone.