Les Sittler wrote:
My understanding is that the car designation RB stands for “Refrigerator
Bunkerless” meaning a car without ice bunkers and that RBL stands for
“Refrigerator Bunkerless Load dividers” for the appliances within the car.
That’s my memory from working at FGE.
Almost. The ORER says that RBL stands for "Refrigerator Bunkerless Loading devices." (Not all loaders had dividers.)