You are missing the point. Apple falsely constrains their supply on the best products to "create" additional excitement. They want people scrambling for supply and they want their resellers committing to things in order to get supply. It is genius!
I would hope they would load up the carriers with product. That is the best way to sell them.
The thing you want to think about is Weeks of Supply (WOS) in the channel. If that increases (for iPhone that is ideally 3-4 WOS of supply) too much quarter of quarter, than you have an issue. However, I've not seen that with Apple for many years.