What is the point of a boxcar with a plug/standard door?
And also
and no one at work knows anything about heated boxcars, what are they for?
Combo door cars were made to have a wide opening for loading when needed. When not needed the plug door fits flush on the inside so the car can be loaded like a conventional car.
Heated cars were \are used for things like potatoes than cannot freeze in the cold weather. Some express cars had charcoal heaters so they could be used for perishables