Since you mentioned the PRR caboose - here's a picture of a number of the Flynn era prototypes and other cars.
The prototype PRR caboose is in the upper left hand corner. Next to it is a prototype CP side door caboose.
The next group has two prototypes - side dump NYNY&H and a side dump PC.
Third line has a prototype Sunoco tank and an NYC high side gondola
Fourth row - prototype Sunoco boxcar, concept CNJ hopper, and prototype CNJ hopper
Fifth row - prototype WP reefer, WP Boxcar, and production WP boxcar
Bottom - a concept and a prototype dummy searchlight cars
The rest of the cars are either production, test shot cars made from CP passenger car scrap, a catalog mockup, or just test shot cars made with standard production tin.