Help dating this photo

Clark Propst

I figure the best way to date this photo is to asked when the NYC did away with their S prefix? Sure appears the closest hopper's number starts with an S? The hopper in front of it is a panel side. A 1930s aerial photos shows the stock pens, they are gone in a 1950s aerial.

Any help would be greatly appreciated,
Clark PropstĀ 

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