Some thoughts. First, as far as I remember, POLA did not make Atlas Cars. POLA sold cars under the AHM brand name. they had a 40 ft box, sort of 1923 ara, a steel reefer, a 40 gondola (now in the Lionel line I think), and a 40 ft flatcar. they also had a bobber caboose, a european style little switcher and the Fairbanks Morse A unit cliner. for steam they came out with the 2 4-4-0s, an IHB 0-8-0 and a "casey Jones" 4-6-0.
Atlas was made by Roco in Austria. So it says POLA on the body, it is not Atlas. Atlas had a more modern 40 ft boxcar, a 52 ft gondola, a plugdoor boxcar they call a reefer, and an Ore car. they had a bobber caboose and a wide vision modern caboose. they also did small switcher based on a US Plymouth, and they did the common F9 A unit. The Atlas freight cars at least are now in the modern Atlas O train man line. I don't know about the cabooses. Atlas in that era, never did a Flat Car.
The santa fe boxcar in the photo above looks to me like a POLA/AHM product. Atlas cars all had stirrups on the ends, that car does not. It could be broken off. However, the Atlas car has sort of a unique roof with a diagonal panel reinforcement formed in each panel. That car does not appear to have that. The atlas car is also a little taller since it represents a newer prototype.
So given the photos and the reference to a flatcar in the group, I am guessing the cars are from the AHM line which came out about the same time.
