The books are printed in China, so they're stuck in port on the west coast as the dock workers are slow working as part of their strike. They'll get out eventually, but that has to do with the dock workers and customs at the moment.
So yeah, they likely pushed back the NA release date.
The Strike sounds like it will lift in the next few days.. (Go check out a News site). But The North American store as a hole is missing allot of things currently.