While publishing delays are common, I still see September 13 as the date on Amazon, for both physical and digital versions for the US (and Amazon UK shows Sep. 13 still for the physical book and Aug. 30 for the digital version).
Having ordered way too much stuff (including pre-orders) on Amazon, I've found that they'll often send out e-mails with changing info about estimated delivery dates. I think it has more to do with their distributor and is sometimes simply a case of not knowing if they'll get the book early enough to be able to get it delivered by the release date. So the date *may* still be Sep. 13.
On the other hand, sometimes the release date *does* change and Amazon, instead of actually just changing the "release date" on their page, simply shifts the "availability" of the item. So I've seen cases where say, you'd hit Sep. 13 and the book is delayed until Oct. 13, but instead of simply changing *that* date, they keep the Sep. 13 date and change availability to "ships in 2 to 4 weeks."
Dunno if it was temp art or fan art or what, but Amazon UK has a separate listing for another version of Mike's book (with a Sep. 1 release date), which only has Mike's name (no mention of Hirsch) with different cover art: