I know I should not be cynical
But I still think, for worldwide Public PR Reasons, Apple will, if needed, balance supply with demand.
Even if they have 50 million made, they won't release them all, so that all sores has a mass of stock any no one every runs out.
This will look, to the media/press as though demand was lower than expected, loads sitting on the shelves unsold.
Likewise, they don't want thousands of customers walking away unable to buy them, when the actually do have more, being deliberately held back in warehouses somewhere.
Ideally you would want to balance it just about right, so it looks like they are in short supply, due to "amazing sales, better than expected" and yet, no so short you upset customers too much.
If this really is controlled in this way I don't know.
But seeing how much time, effort and money Apple have put into this new category launch, and how much they REALLY don't want it to look like a flop, whatever the demand, having such a strategy in place would not surprise me at all.
After all, this is what supermarket food stores do all the time, they keep stock fresh in storage, and only release it to stores as and when needed.
Hence, the cynic in me, suspects that supplies will be tight, and sales will be better than expected (the public shall be told later) irrespective of how many are actually made/sold.