I remember seeing a floor plan of the 4S a few days ago online and it had stairwells in the same place as the Mandalay Bay. I can’t believe they don’t connect, otherwise how would 4S guests get down all the way to the ground level to exit?
Maybe they open freely only out into the stairway for security reasons, so an accomplice up in the 4S would have had to stand by and open the fire door upstairs in order to let Paddock come him.
I think you’re right - they probably don’t open freely in-to the 4S, but could be exited out-of by 4S peeps.