What is it that you think you see there that makes my comment "horseshit"?
The only thing missing from that west facade is the final layer of perforated aluminium veil cladding (the framework of which is in the process of being installed) and a few more sections of the eaves. The open areas that you see are meant to be open (though they will be covered by the veil) because they contain only plant. The perforated cladding will allow airflow and enable cooling.
Same goes for the other three facades to varying degrees. Very little of the remaining exterior work is critical. Not all of it is required to have reached completion in order for interim safety certificates to be issued. Likewise the roof. Nigh on completed. Likewise the stadium bowl. Just 20% or so of seating to be installed (they can install 5K seats a day if necessary) and the turf to be laid (a 3 day job, max). Even work on public areas around the stadium is well advanced.
Still a fair bit to do internally. That was always likely to be the biggest concern. Even so, internal fit out can, and usually does, come together amazingly quickly as the deadline draws near. No doubt that there would have been some non-critical elements of the stadium unfinished by 15th September but the stadium would have been safe and useable were it not for the issue highlighted by the test event.
And if suppliers and contractors haven't been paid?