IMO, it is quite unlikely that customers backed out in droves after their cars were built. Tesla makes good effort to deliver all orders by the end of quarter. And then release a new upgrade or refresh, making sure earlier orders got delivered before that.
If you add up the quarterly production and delivery numbers from the past, it will become clear that Tesla has been building thousands (~6-7K now) of excess inventory cars for rush sales near the quarter end. This is obviously my best guess, but it is very reasonable.