Ok so just to confirm a few things for those who might benefit from knowing:
I've got off the phone to an Apple rep in the UK because my order wasn't showing up online when I tried to search for it and I pathetically got a bit panicked.
First of all, she basically said because the system is so overloaded at the moment, some parts of the site regarding order status etc aren't working properly, so if you click your order number and it's not being recognised or loading or whatever, don't panic.
Second of all, I asked what the delivery date estimates really meant and she confirmed that any orders made before 9-9:30am this morning (UK) were in the 'first batch' and were guaranteed either BEFORE or on the 21st. (She wasn't shy in reiterating that they could arrive before the launch date!) She added that those who got a 21/9 launch date delivery confirmation would DEFINITELY get them then and this date wouldn't change or slip back because "Apple didn't do that to their customers".
After 9-9:30am, delivery dates were pushed back (2 weeks) because launch date pre-orders sold out (as we know).
I'm sorry to say that those who got a 2 week delivery date from launch unfortunately won't be getting them earlier than that, as some people here have speculated. Those who got a launch day date will definitely get theirs then.
😎