Why the second floor lunch room encounter could not have happened

[Albert Doyle]

Of course, if the pneumatic door closer on the vestibule door was a slow closer, and neither Baker or Truly saw the door closing, it would make a very good case for Oswald arriving at the lunch room via the hallway to the right of the vestibule door, should the 2nd floor lunch room meeting actually have occurred.

Or 'Oswald' being in there the whole time according to Carolyn Arnold.