Are you sure about that? I see 2 overhead door openings on the first floor layout on the west side.
Yes, but they open up to a loading dock at the west side of the building, as can be seen on this photo Dan posted earlier

If you look where the yellow line ("Oswald's pressumed escape route) starts, there is a door providing access to the basement area under the loading dock. I think there are more doors like that going north, but I am not sure. In any case, for Shelley and Lovelady to have entered through a door at the west side, they either would have had to take the door to the basement or climb on top of the loading platform and enter the first floor directly.
Am I sure? No, but it seems more logical to me they would go through the basement door and climb the stairs up to the first floor....