I'm going to engage in pure uneducated speculation here: What if all they do in advance is put the hardware together?
As they receive orders, they load the latest and greatest firmware, then they stick the camera in the box and ship it.
Almost there. They build the hardware first, which had been finalized
at some earlier stage. Sample copies from this production are tortured
and software is being finetuned up to a certain point before launch
time, when they freeze a release version and load it onto all those
pre-built cameras that they then send into their distribution channels
across the world. We all have seen them announce a first shipping day
and stick to that all over the world.
This isn't speculation, we have seen them doing it in the past over
and over again.