Bill,

As Tony Thompson indicated, if in a passenger train and loaded, they would be iced by an ice truck with a lift body while still in the train.  That was to save the time of cutting the express reefer out of the passenger train, taking it to the nearest icing facility (probably miles from the train depot), icing it, and returning it to the passenger train to continue its journey.  So, it would be unlikely for a loaded express reefer to be iced with freight reefers.  OTOH, if the load called for pre-icing, I imagine the express reefer could have been pre-iced at an icing facility in a freight yard with freight reefers. 

Tony (or others) certainly are welcome to chime in with their take on this hunch of mine.

Todd Sullivan