I always imagined shops in China got out the calipers and made measurements from scratch every time a new iPhone was released. Never knew Apple made it this easy to manufacture Minion iPhone cases
The big manufactureres pay or just simple acquire the leaks.
Commoditize your complements. Wide choice and availability of accessories benefits hardware sales.
They probably still do, if they have the device, because you definitely want to make sure before creating the not-cheap-even-in-China tooling.
As others have mentioned, these are more useful for when they don't, i.e. before the actual release.