JohnM,
Problem is that if, as Stroud document indicates, that Garner was following Adam and Styles, and was close enough to hear them going down the stairs and then sees Truly and Baker come up. It leaves a very small window for Oswald to somehow sneak past Garner. It isn't the girls on the stairs that is the real challenge but Garner at he rear of the 4th floor. Garner's time could have been confirmed by Dorman, who is usually held to be the fourth of the ladies to move but uses very immediate language in regards to her following Garner and uses the word "run" to describe her movements to where Garner was.
The 2nd floor meeting is constrained by Truly and Baker's ascent time and Reid's ascent and crossing paths with Oswald.
I haven't read "Girls on the Stairs", but does anyone know if Dorman was asked if she saw Truly and Baker going up?
My issues is not that I can prove that Oswald couldn't have used the stairs, but that the investigators should have confirmed the stairs were clear for him to use.
Having not interviewed all the staff between the 2nd and 5th , on if they could view or where viewing the rear stairs , we can have no certainty that the stairs where clear for Oswald to traverse.