The builders photos may help with an explanation of why so many vents. The cars had a "Saloon" at each end which is what in the blue print specs in our files the wash rooms/toilet closets are called. So a vent for each of these. The cars also had a stove at each end, so 2 more vents. They had 4 sets of double oil lamps, so 2 chimneys per lamp set equals 8 more vents through the roof. Notice the ventilation grills in the ceiling of the builders photos. Since the cars did not have a clerestory these vents were provided for warm weather ventilation. I am not sure how many of these vents in total, but I think this accounts for the additional roof penetrations.