I have been looking online for some definitive information, not finding it there, thought I would ask the following:  In the first decades of the 1900s, there were two types of roof hatches for refrigerator cars.  One had an extension of the running boards with the ice hatch offset toward the car end; the platform could hold individual while they were loading the ice.  Second did not have this platform, but simply the ice hatches directly on the car roof.  (The Ambroid express reefers and Train Miniature models have the platforms, the Sunset and Accurail models of pre-WWI reefers do not).

I imagine that the explanation has something to do with (changes) in the roof construction but have not found documentation.

-- ray hutchison